Well indeed this error happens to me too almost everyday, to avoid it I first drive to ammunation, try opening the menu and if I get stuck I use /kill and /taxi 4. It is really annoying, and when you get stuck, and, as Richard says, after getting stuck if you try /buyweapon it returns "SERVER: Unknown command.".
Someone told me it could be something related with the lag/ping/response delay from the server, since I have experienced this bug in other servers with the menus. But I think it's related with the SA:MP 0.2X, because in other versions I never had that problem.
As a suggestion, I think one solution could be when the menu spawns, wether entering the skull or doing /buyweapon, the player can be controllable, so, if it gets stuck the menu just dissapears but the player still can move.
Oh, and I also had this issue in the LVP 2.90 betatest