I can't import .java models

I've noticed that when I import a java model into my resources, there's an error which says that a model which is called "Modelcustom_model" already exists, although I have never created a model with that name.

I know there have been some other users who have reported on this, and I know there have been given solutions to this problem, but I just can't understand them and what I need to change in order for it to work.

Any help appreciated.