Why does my task bar refuse to hide?

[Al Dykes]

I prefer the "auto-hide" setting for the task bar. The task bar will
behave properly for weeks and then for no apparent reason cease to
hide. When I go to the task bar properties panel, the appropriate box
is still checked.

I can generally fix the behavior by unchecking and checking the
auto-hide box but not always. Right now my task bar is always visible
and I can't fix it.

This is a W7 system but my XP systems occasionally do the same thing.

Can anyone point to a solution?

Thanks.