I have been using Audicity 2.0.2 successfully for several weeks. I have Windows 7. Today I did a 3.30 minute voice recording and when I try to save the file, it tells me that it is unable to save and says the disk may be full. It isn’t as I have over 600 hours available. I tried saving to a different folder to no avail. It will let me export as an mp3 and save that file just fine, but will not let me save the AUP file. What do I do next?
Karen 
Are you sure that you are using Audacity 2.0.2 and it’s not an older version that still happens to be installed on your computer? (You can check by looking in “Help > About Audacity”). I only ask because this sounds identical to a bug that was fixed ages ago.
If this is an important recording, Export a WAV file as a backup before you go any further (WAV format will give you a near perfect backup - better quality than MP3)
If it is 2.0.2 that you are using, then I’m unsure what the problem is.
Where are you trying to save the project?
Are you saving to a local hard drive? Do you have write permission for where you are saving?
Try using a project name that is lower case letters only.
Try opening the Metadata Editor (In File menu) and use “Clear > OK” to ensure that all fields are clear.