There might be another reason for that problem.
You wrote that it doesn't work with zip or exe files and some graphics. The reason could be the limit settings in php.ini.
for example
post_max_size = 1M
upload_max_filesize = 1M
That will cause PHP just to stop without any data sent back to the browser if either the posted data or the size of posted files exceed that limit.
You (or an administrator) might need to increase these values.
Thomas