If at first you don't succeed

I'm currently running a Server 2003 network with a mix of 9x, 2000, and XP hosts. Just recently users began to notice that they could not send Outlook e-mails or open web pages until they attempted one more time. I haven't done anything special and users have not reported anything either (but then again, you never know). The antivirus did not detect any viruses after scanning, but it did detect the following threat on three separate but related files: Hacktool.Pwdump

Could this be the source of the problem?