Everything compiled fine and the app is running well. However when I attached the debugger to w3wp.exe and however over variables, no value was being shown. Ctrl-Alt-Q on one for Quick Watch revealed the problem.

error CS1704: An assembly with the same simple name ‘###’ has already been imported. Try removing one of the references (e.g. ###.dll) or sign them to enable side-by-side.

Error seems straight forward enough. Help points to fixing references as the error would suggest. This only just started happening. And not just me. So it must be a code change right? Looking through version history, everything looks innocent. I check the references and they are all fine. So I must have some messed up assemblies somewhere.

Rebuild.

Clean. Build.

Clean entire workspace. tfpt treeclean

Restart visual studio.

Rise & Repeat…

No avail. Both my git and TFVC workspaces have the same problem.

Reboot computer in case of cache.

Then I delete the Temporary ASP.NET Files for the web site in C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Temporary ASP.NET Files.

Bingo! Some change must have caused a duplicate to be place in there somehow. Not the best resolution, but as least I can inspect the code with the debugger again.