Annoying Work Offline Box

While switching between web sites…I frequently get a box that pops up titled: Work Off-Line. No connection to the internet is currently available… and gives me 2 buttons to either to “Work Offline” or “Try Again” About 2/3 of the time it re-connects without a problem. The other 1/3 everything seems to slow down and often requires a re-boot for everything to run smoothly. Is this an XP problem? Any suggestions?