I have seen this happening before. If you are following the entire tutorial serie, then at one point you changed the following line in the fpsplayer.lua to this. (around line 290)
--Use the object, whatever it may be
usableentity.script:Use(self.entity)
The reason why it probably no longer works:
When Leadwerks has an official update that changes the FPSplayer.lua, it replaces your lua file with the new one. That means that all your changes so far, are now gone (You can access the backup which is in the same folder). If an update has been pushed by Leadwerks that changes the script (somewhere last month the player script has been updated), then the line looks as follows:
--Use the object, whatever it may be
usableentity.script:Use()
It is a quite annoying so I am going to switch to a separate FPSplayer script in order to prevent this problem from happening again.