Misbehaving 1st gear

[mingmong]

Hi,
I was parking the car yesterday, trying to get close to the curb by reversing back and forth in 1st gear. Did this a couple of times but then on the next attempt couldn't get out of 1st gear. Clutch was depessed, engine running, but the gear lever was really stuck. Eventually, with rather a lot of physical effort, managed to pull the gear lever out of 1st and find neutral. It made an alarming 'pop' but no crunching noises. Parked up and went home. Next day performed the same manuover with no problems at all. Any ideas as to what this all might be about? The car was hot (after a 3hr trip) when it misbehaved, cold when it was tested again. Any thoughts always appreciated for some peace of mind

Cheers -M

PS Cars a 1977 Carrera 3.0