Thanks for reporting the issue.
If you need to use a newer version of dbghelp, you should recompile OpenCppCoverage otherwise you have a mismatch between .lib and .dll files.
Supporting /DEBUG:FASTLINK is something I will work on it for the next release (No idea when it will be ready).
In the meantime, is it possible for you to not used /DEBUG:FASTLINK when you want code coverage?
to have more information about the dependencies.
I hope this will help,