My volvo 850 transmition cut out on me. For a while the arrow on the dash was blinking and it would switch to limp mode. I brought it in to be looked at and they didn't find a problem. Last time it happened the car slipped out of gear and didn't move at all. I had to stop the car and wait a few seconds then start up again. After that, everytime I came to a stop I had to stop the car and restart. What's going on??

The transmission indicator light blinks. The car changes gears, but will not go down to the lowest gear when you stop. If you cut the car off and start it again, it goes into the right gear, and seems to change properly, until you stop. What is causing this?

Any time the transmission goes into the limp mode, it generates an error code that tells what caused it to go into limp mode. It could be something as simple as a loose connection on a sensor for the transmission computer. The code would explain which sensor was sending the correct signal.
By restarting the car you are resetting the transmission computer, clearing the limp condition.