Hi, thanks for posting!
NCrunch is carefully designed to isolate projects in 'workspaces', which are effectively just directories in a different area of your hard drive. In doing so, any activity from NCrunch shouldn't interfere with your foreground solution in Visual Studio, even though builds will certainly be run throughout your usage of VS.
Generally errors like this one are a symptom caused by absolute file path references that point out of the workspace and into the original solution directory. Make sure you don't have any absolute file path references pointing to 'myassembly.dll' in your solution directory - as this can cause some messy behaviour. An easy way to find these references is usually to just run a global search over your codebase, or to try renaming your solution directory then running your tests ... most likely this will cause the offender to throw an error that you can use to track it down.
I hope this helps.
Cheers,
Remco