What can be cause of 2004 Toyota Tacoma 5spd transmission not engaging gears when engine is cold.?

2004 Toyota Tacoma 5spd, cannot engage gears when engine is cold (If engine is off all gears engage) Once truck idles and warms 10-20 minutes it then will engage all gears. What can be causing this?What can be cause of 2004 Toyota Tacoma 5spd transmission not engaging gears when engine is cold.?I think there's a safety device that locks all the gears so the truck will have time to correct the temperature of the engine before it can run.