Vista - Logged in as Administrator, but lacking rights, apparently

Some programs (e.g., Spybot) tell me that I need to log in as an Adminstrator
to run them. But I'm already logged in as an Adminstrator. What gives?

Here's the error message from Spybot:

"You are missing administrator rights to perform this action. If you need
to do this, please run this application elevated as an administrator."

Only recently have I started having this problem--within the past couple
weeks, I'd say. And I've been running Vista on this computer for nearly a
year.

Thanks for any help.