Open up your upload.tpl file and find the following code:

Code:
<input type="hidden" name="MAX_FILE_SIZE" value="1048576000">
Remove one of the zeros at the end so that it looks like:

Code:
<input type="hidden" name="MAX_FILE_SIZE" value="104857600">
I believe that this was supposed to be like the second one from the beginning, but someone may have fat-fingered the number (this is based on the fact that 100MB is the file size that is listed in the template by default). What this is intended to do is to pass a variable into PHP which tells PHP (from the browser side) what the maximum allowed file size should be. If a person attempts to upload a file bigger than this, you'll get a browser based error that the user can see before the upload even takes place. Without this (or in our case, this being incorrect), the file proceeds to upload until it hits the server's hard limit. When this happens, PHP refuses to accept anything further and a connection timeout is eventually displayed.

For your notes, the number is your maximum file size in bytes. The new number, 104857600, is 100MB in true bytes. The original number, 1048576000, is 1GB in true bytes. As originally written, you would never get an error until you upload a file bigger than 1GB, lol.