Is there any answers on this? @benFF confirms he is having the same problem..... I have noticed that while XenForo is a fabulous product.... support for the addons especially Media Gallery is nowhere near the level it could be.
i assume that you were able to solve the issue of moving a private album.
Nevertheless, I will briefly show the solution, because surely at a later time other users will come across this node. I have created a graphical representation (see attachment)
Step 1 = The registered user should open his private album area -> Step 2-4 = Open album category (content / content directory) and move it to the desired category.
Hehehe... you should try another script that I have a license of. I've seen posts over there requesting assistance not be responded to for over a year. The developers response was "submit a ticket". That was the ONLY way you got any developer support for anything remotely complicated, and rarely did other license holders respond because they were "point & click" admins.