stuck in 2nd

whilst driving home from work the other day the transmission got stuck in 2nd gear. i was in rush hour traffic so it wasn't like i was power shifting or anything. when i went to shift into 3rd the lever wouldn't move much and as i pushed it forwards i could feel a pulsing through the lever. luckily i wasn't far from home and with crappy orange county traffic only having 2nd gear didn't make much difference to the time it took to get back home!

when i got home i disconnected the 1-2 shifter rod and could move the shifter freely. i tried moving the lever on the traansmission with vice grips but was unable to do so.

anybody have any ideas what's wrong? is it likely to be something i can fix by removing the side cover or is the trans going to have to come out?

thanks