I\'m running WP 3.0.1 on a shared host using PHP5. I\'m having issues uploading files that are a little larger via the media uploader in the admin section of WP.
Eve
The problem, as you've already inferred, is in the size of your file upload. Just to remind you, HTTP isn't really built for transferring large files ... it can do it, but not always, and not very well. You're running into an issue where your host is cutting off the transfer because the file is too large. It's most likely a server setting somewhere that you don't have access to.
Since "they don't support 3rd party scripts" I'm guessing you're in a shared hosting environment, which is why something could change on your server without you doing anything. Possible solutions: