I don't really understand the technical background here, but I noticed the following problem:
When in VisualStudio, check the Project Properties, and under the Database Tab you have the Connection string.
It looks something like this:
Data Source=[ServerName];Initial Catalog=[DBName];Integrated Security=True
I unfortunately didn't copy the connection string from before - but instead of Integrated Security=True
it had something with ...User...
. I think I had UserID=sa specified, but don't remember exactly, and I don't know why the connection string was set that way.
I clicked the Browse-button and refreshed the connection (chose my DB and clicked 'OK'). The connection string for the project was reset with the Integrated Security=True option
set.
I don't know if it matters, but in my CLR I'm connecting to the db using "context connection=true"