What's with this Limited Access Box on Logon

Today's challenge...

Am running XP Home with two users. When logging on to the account as the
administrator a box pops up that says something to the effect of
Unable to logon-limited access account. I simply click ok and the computer
boots up without difficulty but this box thing is most annoying. Any
suggestions as to why this obviously incorrect box appears and more
importantly, how can I get rid of it?

Thanks for stretching your minds on this one.