Ghost Buttons -how do I kill them?

You know when you open a program, a button appears on the task bar...then when you close the program, the button disappears... Well, for the first time, the button does not disappear.

I have had this one annoying button sitting there for a few days, with no identifying feature as to which prog it is related to ...it is just a light blue [in contrast to the darker task bar] button with a small dos window as the identifying icon in its usual place to the left of the button ...which usually means XP cannot associate a program with the button...there for no "hook."

I have done all of the obvious things, as far as I can tell, such as:

I have shut down system restore to clean out the restore points.
I have scanned for any malware, etc..
I have down the usual maintenence, as I am an old hand at maintenance.
I have scanned the registry for any reference to the task bar that might give me a hint re: where to start...but nothing seems to be available.

ANY SUGGESTIONS?

Edited: 07-23-07...SOLVED...go to last post