Almost every day, I am seeing the following error in Explorer

HTTP error:
Transport error (#12007) while retrieving data from endpoint ' /ajax/session,php': Unknown HTTP error #12007
[Okay]


When this error pops up, from that point on, every time I open or close a browser tab, I get another error

Control Point
Invalid handle
[OK]


Which I have to OK before the tab will open or close. This continues until I reboot.

I am running Windows Vista with IE8 on an HP Touchsmart PC. As I said, rebooting fixes the problem temporarily but it always reappears, with the same results. I have tried clearing my cache & temp files, etc. & have ran CCleaner to check for any "unwanteds". Also running Avast virus protection.

Any help with this would really be appreciated! Thanks!!