"I installed XP MCE".

What does that mean, installed on a new computer, or installed over another Operating System?

How did you install it, by re-formatting and installing from the CD, or by upgrading? Is this a genuine XP MCE CD?

XP Media Center uses "add ins", and this error message when Media Center is launched can show a problem with one of the add ins. So, I would start looking at those. This article may help;
Aaron Stebner's WebLog.