This error (104)Connection reset by peer: mod_fcgid: error reading data from FastCGI server started to appear in my apache error log whenever I tried to upload a file. Apache seemed to be working fine with static html pages, it was only when I tried to upload files that I had problems.
Searching for a solution suggested a whole series of possible causes all revolving around permission problems. Since I had not changed anything on the server for a few weeks, and everything looked fine permission wise, this did not look to be the cause. After checking everything I could think of I noticed that the disk quota allocated by Virtualmin was only 1 GB and that I had used nearly all of it. I upped the disk quota to 10 GB and the problem was fixed. I hope this helps someone.