I recently had to use SQL Compare to create a rather large add new and update deployment script.
I was pleased that it picked up User Defined Types in addition to the normal tables and stored procedures.
But it did not pick up the permissions for the User Defined Types, and that was a failure point when executing the stored procedures.
This was my first time working with User Defined Types before, and I thought it odd they needed permissions at all. I did not apply any in the development environment, and they worked there.
But the error was clearly a failure to apply Grant Execute to the User Defined Type.