I was also having the same problem during file upload some 3-4 months before.
The call was going to servlet but in the front end i was getting some error (#2038).
Later i found out that my code was having some exception in Servlet and then it was not getting processed correctly. I does not remember what the exception was, but when i solved that exception, the error was gone.
b/w are you using commons-file-upload to upload the file?
Regards,
Anoop