I didn't open your file to check, but the Path mate in the advanced mates is used when you have two different parts. You blocks are probably part of the same sketch, so the same "part", hence the error message.
I don't use blocks much, but I think that you would just need to establish sketch relations, such as coincident, between points on your blocks.
I've never done a Motion Analysis, so don't know what is happening. I would expect that to work on parts in an assembly, not on blocks in a sketch.