Cant upload pictures to Media library plus

Hi Support team

When I try to upload my picture to my website Media gallery using Media Library plus I get the following error. Can anyone tell me what to do about this and why it's happening?

<TITLE>Web Acceleration Client Error (509.3) - Upstream TCP Receive Failure (Bypass Proxy Server)</TITLE><B><font face=arial color=#3642a2>Web Acceleration Client Error (509.3) - Upstream TCP Receive Failure (Bypass Proxy Server)</font></B><font style=normal face=arial size=2px><P>The Web Acceleration Client detected a TCP connection failure while receiving data from the Web Acceleration Bypass Proxy Server. Retrying the web page may correct the problem.<P></font>