Some images cause: Error 500 - Internal server error

[Fastbird]

When uploading images to a users personal gallery, they are experiencing a 500 error, in what seems to be a random order.

User attempted to upload a picture with these dimensions and filesize:

799 X 571
634kb

The limit is 1024x768 and the filesize upload is limited to 10MB, so there is clearly no issue with restrictions.

It's happened to me a few times too. Any idea what could be causing this?

[Dismounted]

500 errors usually indicate an error with the server configuration. Possibly a misconfiguration of mod_security maybe?

[vBsquad]

Please post a link to phpinfo() and if you are using mod_security please post details of your configuration.

[space?]

more Information.
Only images _can't_ create an Err500, there has to be another component.
Please post your .htaccess, and if you like to - your logs.

[Dismounted]

It's uploading images ;) - so it's the PHP file.

[space?]

It's uploading images ;) - so it's the PHP file.
...or the php configuration;)

@Threadstarter: Have you checked you chmods?