Cannot complete uploads in phpBB forums

Hi!

I am a frequent user of http://forum.mflenses.com (based on phpbb). Recently photo uploading stopped. Tried Firefox, IExplorer (v6) and even Opera. I have Win XP SP1 so also tried on different computer with XP SP2. Uninstalled all Java and reinstalled it. Drag and Drop upload Java applet (http://forum.mflenses.com/jumploader.php) starts uploading but gradually stops around 20Kb. Upload picture (http://forum.mflenses.com/uploadpic.html) without success. I disabled all firewall protection...

Google Chrome response:

"This web page is not available.
The web page at null might be temporarily down or it may have moved permanently to a new web address.

Error 103 (net::ERR_CONNECTION_ABORTED): Unknown error."

Opera says:

"Connection closed by remote server
Check that the address is spelled correctly, or try searching for the site."

I have no problems on other pages. I upload in Picassa or DeviantArt large photos without any problems.

I isolated the forum platform as somehow refusing my uploads. Is that possible and can something be done?