Virtual Memory full in Internet Explorer

I recently install Symantec Web Security on my server. This requires that all clients have their IE set to Proxy server. I changed the Group Policy to force a proxy server for all my PCs. Everything works fine except for two PC's. These two PC constantly get a "Virtual memory Full" message when starting Internet Explorer. The entire computer is hosed until we end-task IE. Once we do that the computer is working fine again. I checked for viruses, downloaded all the windows updates and nothing seems to fix the problem. Both of these machines have over 4GB of hard drive space available. Help!