B2000 transmission problem

I got an 2007 Mazda b2200 5speed truck. I went to go stop at a stop sign it was in 4th gear. And out of no where it wouldn't come out of gear. It was stuck in 4th. I got it towed home. Anyone got any idea what this might be? I have had no trouble out of it at all till this. No noises made at all

When mine did that it was 5th gear which had seized on the shaft I dissassembled it cleaned up every thing.Polished the shaft d lit everything back together. No manual just Comon sense and it was easy.