Unable to shift in 1st and 2nd gear

[RcMlndz@aol.com]

While driving my 72 TR6 after a complete gearbox rebuild with no warning, all
of a suden  im not able to shift into 1st and 2nd gear. The gearbox doesnt
make any strange noise. It worked just great for the first 20 miles or so. It
has a new magic clutch kit and all new gearbox bearing syncros trust washers,
etc.

3rd and 4th gear are just fine.

Is not definitely the clutch because im not able to shift in 1st and 2nd gear
when engine is off.

Any help would be appreciated

Ricardo