can't network after full drive sharing

I've tried looking around to see if anyone has experienced this...

Running Windows/XP SP2 Pro on our laptops.
On one of the laptops, I can't get it to share across the local network.
They are all pretty much setup the same way,
and we are pretty familiar with the various speed bumps of sharing.

I THINK that this is the result of at some point in time
We shared the entire C: drive - got the warning msg - and did it.
And it proceeded just fine.... after that - we reset the sharing
to just point at a couple of sub-dirs... and now it does not work.

I can see it in the "Windows network",
I can click on the computer icon and drop to the next level,
but at the lowest level - we get an error message about "permissions".

I'm pretty sure that's a bogus message, as the laptops are setup
with the same users, etc - and it's just this single laptop
that refuses to share.....

Anyone run into problems after sharing the entire C: drive,
and then going back to just sharing a few sub-dirs ?

I don't know what else to look for....