The problem: The task bar gets 'stuck' in an open position. It opens when a box message ('You need to update' or 'This program needs attention') opens it to get attention but once the box is cleared, there's the task bar. NOTHING short of a restart will make it go away.
Extent: It existed in XP and, according to several bulletin boards, it still exists in W7. I think it has suddenly gotten worse but it has been a problem for a lo-o-ong time. I find it in threads going back to 2001. I find it in W7 threads.
Microsoft's solution: ...is stupid. "Uncheck 'Lock Task Bar' and then turn on 'Autohide'". Clever people at Miscrosoft. This, of course, does NOTHING!
This is a major PITA. My solution has been to run the task bar along the left side of the screen so I can finish some work before having to reboot. Someone on this forum must have a better solution. Anyone parroting the Miscosoft 'advice' deserves permanent expulsion to a parallel universe in which no algorithms function.