HELP! Transmission / Clutch

All the sudden my car doesn't want to shift into reverse! I've had very 
little problem with this in the past. An occasional; put it in first and 
nudge forward, then go back into reverse ok but, I thought that was pretty

normal. It hasn't been doing it allot lately but when I got home tonight
and 
tried to back into my drive it pretty much refused. Several attempts
failed.

Is this the beginnings of a clutch going out or a transmission problem?
What 
do you think?

Clutch and master cylinder were rebuilt with in the last 20k probably 
(supposedly anyway. I was out of town and had to get it done in a pinch at
a 
dealership).

Help!
Chris
99BBB