I was attempting to debug a stored procedure that calls CLR functions (however this story can be told for any CLR object) and the debugger would simply hang.

There are two steps to get around this issue:

First is to disable and re-enable CLR debugging. To do this, in Visual Studio right click the SQL Server and uncheck the Allow SQL/CLR Debugging line.

Then re enable it, where you will see the following dialog where you should press Yes.

The second step is to disable affinity for multiple cpu machines.

In SQL Management Studio, right click the server in the tree, and go to properties. There click on the Processors, Uncheck the Automatically set processor affinity mask for all processors:

This worked for me. I am wondering if there is a hotfix for this?