I've been trying to get NCover to run successfully on Vista Ultimate x64 on and off for the last month. We're still using one of the free versions of NCover available from here, so there is no built-in x64 support. I came across this post today that mentioned using corflags to set the 32BIT flag in both NCover and your testing application (the post is describes using NUnit, but this worked for me with MBUnit as well).
Those changes got me past the
Profiled process terminated. Profiler connection not established.
error, but I was then confronted with a new wrinkle:
Index was outside the bounds of the array.
This error would appear at the end of the profiled MBUnit run. I poked around some and found some old posts on the NCover forums talking about this error and how it didn't occur in NCover 1.5.5. So I downloaded 1.5.5 (I had been using 1.5.8) and now all is good - coverage runs successfully!
We're not doing that much with NCover at this point, so I don't think we're giving up anything going with 1.5.5. Maybe someday we'll be able to purchase a current license that supports x64 out of the box.