quartus 15.1 fit Internal Error (always at 35%),bug?

Hi,

I know this is an old post, but I had the same error and found the solution. This error migth be a Quartus bug, but it ususally happens when it tries to fit something that it cannot understand so, instead of generating a comprehensible error message, it just breaks down. The way to find the block that causes this error is to create a simpler design and test each block one by one, until the compilation breaks again. Then you just have to debug the block that causes the error and compile your full design.

Cheers!