"Windows Can't Check For Updates"---Anyone else had this message on their computer? What did you do to resolve it?

“Windows Can’t Check For Updates”——This balloon message keeps popping up after open my computer. I’ve tried almost everything to resolve this problem, but the message still pops up, which means Windows still cannot check for updates. Has anyone else here had this problem? And what did you do to rectify it? I have Windows Vista. I had 2 firewalls going on at the same time recently, so was this causing the problem? I’ve disarmed one firewall already, but the message still pops up.