With what GA said, when you asked your question, was the shifter still in reverse, or had you returned it to another gear? The manual clearly states that you don't shift to R unless something is turning....engine is running or you are hand turning the prop with the engine off. Reason is that down in the lower unit the shift mechanism is a square cog and square slot. The cog has to line up with the slot before shifting is accomplished. If you tried to force it into R without something turning you could/could have damaged your linkage....where has to be determined.....first place to start is to disconnect the remote control at the engine and see if you can run it through the shift pattern from there.....remember turn something when trying to go to R.
On sitting for 10 years, you need to set the engine vertical and after 24 or so hours of not turning anything, pull the drain plug carefully and see if any water comes out (first). Then what color is the oil in the LU? Do you have a magnet imbedded in the drain screw? If so what's on it?
