There are several reasons that you cannot upload a file with a script. The following are 2 possible reasons.

The first, simple enough, is the file size is too large. To fix this just modify the “upload_max_filesize” modifier in php.ini. To determine the location of the php.ini being used by that domain quickly create a phpinfo() page. (simple page with ) this will display the information.

note: remove this file afterwards as it gives information on your server and can be considered a security risk

The other possible reason, and you need to look at your error logs to verify this is if you are getting a similar error message to this:

 mod_fcgid: HTTP request length 138361 (so far) exceeds MaxRequestLen (131072), referer:

or something similar.

This indicates that the apache configuration needs a little tweaking.

do a quick search for the file: fcgid.conf
modify it by adding the following line

FcgidMaxRequestLen 200000000

This sets the limit to 200MB.
Example file would look like:

<IfModule mod_fcgid.c>

<IfModule !mod_fastcgi.c>
    AddHandler fcgid-script fcg fcgi fpl
</IfModule>

  FcgidIPCDir /var/run/mod_fcgid/sock
  FcgidProcessTableFile /var/run/mod_fcgid/fcgid_shm

  FcgidIdleTimeout 40
  FcgidProcessLifeTime 30
  FcgidMaxProcesses 20
  FcgidMaxProcessesPerClass 8
  FcgidMinProcessesPerClass 0
  FcgidMaxRequestLen 200000000
  FcgidConnectTimeout 30
  FcgidIOTimeout 45
  FcgidInitialEnv RAILS_ENV production
  FcgidIdleScanInterval 10

</IfModule>