Windows XP Pro loses Window focus on mouse click

Archived from groups: microsoft.public.windowsxp.help_and_support (More info?)

In the last two weeks, my system which is running Windows XP Pro on a 2.6 GHz
Intel Pentium PC, has begun to exhibit some strange behavior when I click on
a window to gain focus. I can click on the window most of the time; however
after clicking once that window loses focus and I can no longer click and
gain focus. The only way I've found to regain focus is to press Alt-Tab at
least two times before the mouse works in that window again. I have the most
recent version of Symantec Anti-Virus and am using Microsoft's Anti-Spyware
tool. I also went out and did an on-line spyware scan with WebRoot's Spy
Sweeper. Any help would be greatly appreciated.