PDB server error when analyzing .ne core console application

When I try to run dotCover on my unit test application the program runs to completion but then when the analysis is being done I get this:

The application is a .net core console application written in F#. It references a couple of other .net standard libraries that are also written in F#. The units tests use the Expecto framwork. 

Anyone have any ideas what's going on here? If I create a new .net core console app and analyze that then everything works fine.