You can add "If PP doesnt like your jpegtran" to your list of causes for the CGI error.
The reason for the inconsistent CGI error, was that gif files uploaded fine (just didnt try maney of them at first to notice a pattern).
But jpg's cause the error. I removed the path to jpegtran in admin global options (i think thats where) and now jpg's upload as well.
Now, in order to fix this, what is the format of the path so I have it correct? I tried different variations (end slah, no end slash, fwd slash bck slash, include the full file name as well, etc) to no avail. I've asked host tech support to give me the path to their version next.