Please see attached screen shot. This does not happen everytime, but about 60%.
Windows Vista SP2, Audacity version 2.0.2.
The good news is, most of the time I get the option to recover the project I was last working on.
2.0.2 is obsolete - please upgrade to the current 2.0.5: http://audacityteam.org/download/ .
The project audio is probably corrupted - such issues are usually a single-sample clip that you can’t see until zoomed in to see all the samples.
I suggest exporting as a WAV file. If you had more than one track you would have exported each track as a WAV by clicking above the Mute/Solo buttons on each track then File > Export Selection. Then restart Audacity, import the WAV file(s) into an empty project window and save the project as a name you haven’t used before.
If you know the steps to produce the split line in that place and that always produces a crash in a fresh project, please let us know.
Gale
Very simple - you should know how the black line is produced - you work for Audacity. 
The merge line appears when pasting audio from one wave form into another, or, as in the case of my screen shot, generating silence(1.2 seconds of it above) or noise.
Also should I remove Audacity 2.02 before downloading and installing the newer version?
No-one works for Audacity. We are all volunteers.
The split line appears in other ways too, such as explicitly adding it with CTRL + I, or after using certain effects in a selection that includes white space. We can’t see the History of your project to know how the split line came to be there or what audio may have been there before.
There is no general bug (even in 2.0.2) where generating silence at the start of the track then clicking on the resultant split line creates a crash.
So if this crash happens again in 2.0.5 in projects created in 2.0.5, and you can tie it down to a set of steps leading up to the merge and crash, please let us know. Otherwise there is nothing we can fix (at least without getting hold of the actual project AUP and _data folder).
No need to do that. Please see http://manual.audacityteam.org/man/FAQ:Installation_and_Plug-Ins#exe .
Gale
Just to amplify what Gale has said: when reporting a bug it is very important to be able to tie it down to a very explicit (and hopefully short - though not always possible) “Steps to reproduce” the fault - and this should be repeatable (by you - and by us). In particular the developers need the “Steps to reproduce” in ordered to analyze and fix the bug. “Steps to reproduce” is one of the key fields in the Bugzilla bug-tracking system that we use at Audacity.
It does get harder when something like that only happens sometimes, and not others, and no-one can figure the surrounding circumstnces that caused it - these get classified as “moon-phase bugs” - bugs that “depend on the phase of the moon” to occur …
Thanks,
WC
There’s a first for everything, and I can state personally that it sucks being the first! lol
Well, my typical Audacity sessions are pretty mundane:
RECORD/IMPORT AUDIO
GENERATE SILENCE
Click to remove black splice line
AMPLIFY
ANALYZE/EQ
or COMPRESS
AMPLIFY
EXPORT
In mostly that order.
Occasionally I may copy audio from one import/recording into another, which also generates the splice lines on either end of the imported piece. I then click to remove those lines.
The crashing after clicking to remove the black lines occurs mostly after a session has lasted at least one-half to one hour; sometimes longer.
Question: Should I just ignore the splice lines and get on with my sessions?
There’s probably no need to remove the split lines, though if a track has lots of split lines you can “join” the splits all in one go by selecting the track then press Ctrl+J.
“Join” is also in “Edit menu > Clip Boundaries > Join”.
I don’t get split lines from doing that. Have you updated to Audacity 2.0.5?
If you record or import then generate silence at zero (as I assume the poster does) or at the end of the track, a split line is produced.
The poster says
Crashing after clicking to remove the black lines occurs mostly after a session has lasted at least one-half to one hour; sometimes longer.
So presumably any number of the effects that the poster listed have been run across that split line (or across the removed split line). Which is it? A crash immediately you remove that split line after generating silence? Or a crash an hour after removing the split line? If so, why do you attribute the crash to the removed split line?
Or are you removing that split line an hour later?
Gale
Generating silence (or generating any audio) at either end of an audio clip will leave a split line between the generated audio and the original clip.
If I follow the instructions exactly : 1) Record some audio 2) Generate Silence, then I get silence on a new track (no split lines), so I assumed there must be other steps between 1 and 2, such as clicking on the recorded track or selecting part of it.
I was just interpreting what the poster may have done according to the screenshot.
All this is proof that unless the user lists every single action in order 1, 2, 3… that precede a crash, we may not be able to reproduce any problem at all.
Gale
It’s very very very simple: The crashes occur immediately after clicking to remove the black split line.
I can usually click the line to remove it safely for the first 30-45 minutes without a crash. After that, the chances of a crash increase rapidly after clicking black line to remove it. During the sessions, a lot of importing or recording, exporting, and a lot of effects might be used.
Sorry I was not clear in my initial description.
Also, I am very conservative: I don’t update unless it’s mandatory. If something is already working, why “fix” it? 
Well we’re unable to reproduce the issue on Audacity 2.0.5, so perhaps that could be a reason to update?
(though there is no guarantee that updating will fix the problem as this issue was never reported for 2.0.2 - and there were around 10 million users of 2.0.2).
Like I said, I’m a first for a lot of things - something you wouldn’t want to be. lol!
I would suggest you use CTRL + J to to remove the split lines from time to time. By default that will select all the project audio then perform the merge.
Gale
I just used it. It’s safer, although once it produced a “fadeout” of the Audacity window and a twirling cursor(as though it was going to crash) but it recovered.
BTW I have plenty of memory and it is all visible to Windows.
Sorry for the necroposting.
I’m having the same issue as the OP.
Sometimes, when you click the merge line after silencing, it crashes. It doesn’t hang before crashing like normaly a program do. The crash window appear instantly.
Sometimes it happen, sometimes not. But given that we are having the same issue I think it’s a audacity problem. I’m using the 2.0.5. Windows XP.
The reason why it’s very hard to detect a bug is because audacity don’t have a crash log (at least I don’t know where it is), only a start log.
Yes this is a known issue and is listed on the Audacity bug tracking system.
The workaround is to use CTRL + J to to remove the split lines. Select across the splits to be removed, then press Ctrl+J. Note that you can “join” multiple splits at the same time using this method.
The bug listed on our bug tracking scheme depends on joining two tracks above each other into a stereo pair (where one track already has a split line), using “Make Stereo Track”.
If you start with an empty project, Generate > Tone and can make the problem happen at least some times using a set of steps, do please let us know what those steps are.
How are you silencing audio? CTRL + L doesn’t normally create a split line.
Some read and write errors appear in the log, but the log doesn’t persist across Audacity sessions. If Audacity crashes or is quit normally, the log is lost.
On Windows it isn’t possible to get useful call stack traces unless you run a debug version of Audacity from within Visual Studio.
Please be careful on XP. Your computer is exposed to any hitherto unknown vulnerability that appears and can never be patched for it at the system level given Microsoft no longer officially supports XP.
Gale
The steps are:
Open a song or start a new project. Go to the beginning of the track. Click some seconds in the track and drag till the beginning (a yellow marker line will a appear). Go to “generate / silence”. It will leave a split line. Click the line and sometimes it crashes. It’s very rare (it only happened 2 times with me).
It seems that Ctrl+L does indeed generate the silence without leaving the lines so I think I’m gonna use it for now on (I was using “generate / silence”).
Thanks, piau9000. If you do find steps to make it happen repeatably then we can look into it. It may be that any imported file will do it if you click at a particular spot (look at Selection Toolbar at the bottom).
Or it may be a particular project does it wherever you click because it already has other split lines or some other reason.
Gale