I recently got a Line 6 guitar port and have been trying to record using Audacity. I’ve used this program for ages and I love it so was very happy that it was compatible with my guitar port. But it keeps stuttering and missing big chunks out of what I’m playing when recording, plus it keeps putting harmonies out of sync when I know I’ve played them dead on which has never happened before. Same when I’m playing along with backing tracks. Does anyone have any idea of what’s wrong? 
The Guitar Port isn’t keeping up with the recording. This could be due to a faulty Guitar Port, a bad cable, a bad USB port, bad drivers, or trying to record at a sample rate that the Guitar Port doesn’t support.
I think the Guitar Port comes with ASIO drivers, you need to make sure it isn’t using those.
Your best bet is to talk to Line6’s support.
Failing that, can you record using Windows Sound Recorder?
Ok, I’ll have a look at all those things. Thanks very much!
I probably could but I just like Audacity so much that I’d rather use that if I can.
I meant to try recording with Windows Sound Recorder in order to test your hardware using a different piece of software.
You wouldn’t be able to use that program for any multi-tracking, but it’s a useful diagnostic tool when things go bad. If the same problems show up there, then we can eliminate Audacity as a possible cause.
Oh right, sorry. It doesn’t seem to work with that program I’m afraid. I’m recording in Audacity just now and it seems to be fine for the moment. Maybe it’s because I’m recording it in chunks, instead of all at once. I did change the guitar cable and used a different usb port so maybe that’s made a difference. It’s only happening now when I try and play a backing track and record at the same time in the same window. I’m playing the backing track through media player and recording as normal. A bit more work for me in the end, but it’s doing fine for me now. Thank you for your help! 
You should be able to play other tracks while recording one. If that isn’t working then something is still wrong.
The next thing to try is defragmenting your hard drive. If it’s full or fragmented, Audacity can’t read and write data as smoothly as it needs to.
I’ll give that a try as well. Brilliant, thanks!
if you can record only segments but not a whole track i would say that indicates that the problem is with your computers power. you can try free some memory by closing unnecessary tasks, also defragmentizing is good.
if nothing works in this direction, you should consider upgrading to a more powerful computer.
Johnny from guitars101