My chain block wont lower

I have a 1 tonne PWB-Anchor C series chain block. I used it horizontally to remove a tree stump in the garden, and now it will lift , but not lower.
Do you know what the solution is?

Fixed with a moderate tap on the chain driven wheel with a hammer and screwdriver.  Yep, I use old screw drivers as punches, chisels, scrapers, levers, in fact, I find them to be the ultimate tool for abuse