Check the setting 'Maximum download size (incoming in KB)' in Proxy > Configuration > Proxy settings, this should normally be 0 (zero) to allow any size of file, if you have a different value here then this is what is causing your issue;
I have seen there is a bug with this setting, see the post here for more details;
http://www.efwsupport.com/index.php?topic=2943.msg7853Hope this helps.