Problem with Import manager

[Maldrior]

I've got a problem with the Import manager.
I want to Import a Unit, but if I'm going to the folder of it, there are no files. I tried it with some other Units but it didn't work
I have still imported some Units a half year ago or so, but now it don't works anymore. I think the Problem are the files or theres no program on my PC anymore to open the files. It's a ".blp" and a ".mdx" please help me.

Thanks