Visual Studio throws this error when attaching the debugger or just debugging.

Unable to start debugging on the web server. Unrecognized error occurred in the Windows Web Services framework.

I bet your Application Pool is set to not Enable 32-bit Applications.

The setting is in the IIS > Application Pools > Advanced Settings > (General) > Enable 32-bit Applications

or if you know the $poolname, probs need to be admin to…

Import-Module WebAdministration;
Set-ItemProperty IIS:\AppPools\$poolName enable32BitAppOnWin64 true;