I have used snappyHexMesh once
 

I have used snappyHexMesh once successfully. I am trying it on another case now. I have an STL of a building. I created a block around it, the building standing on the floor of the block. When I run sHM, I am getting
fatal flex scanner internal error--no action found
Since there is nothing else mentioned, I am not able to guess where the problem might be. Could anyone guide me on where to look for errors?

Thank you
Prapanj