There are a few suggested "fixes" in this thread:

Hide Taskbar - Vista Ultimate : Windows Live OneCare General : Windows Live OneCare : Microsoft Forums

I tried the fixes suggested. No good.

Thanks.

any chance you have hp printer software, like "hp digital imaging monitor" installed?

Yes I do. I have an HP AIO and the "hp digital imaging monitor" is in my system tray.

Disable or remove it temporarily from tray, see if your problem persists

Originally Posted by JohnQPublic

Yes I do. I have an HP AIO and the "hp digital imaging monitor" is in my system tray.

Another thing that may help-- if you are running a wireless network, right-click on the wireless network symbol and "turn off notification of new networks." This also works as everytime a new network is available (even though you are connected) it triggers a taskbar reaction. Hope this helps!

Try this:

1. In the task bar in Windows 7, click the arrow to show hidden icons.
2. Click Customize
3. Click Turn Syteme Icons On or Off
4. Select off for the Action Center
5. Click OK twice

This has worked for me on (2) Windows 7 Enterprise machines.

Good luck.