Here’s the simplest repro case possible.
SSMS tries to get the extended properties of the table using fn_listextendedproperty. According to MSDN the required permisions to view a table's extended properties is
ALTER on table OBJECT
Your login test should have this permsision as owner of the test table (it is the owner, right?). But even if you don't have permissions on the table, the query for extended properties should return emtpy result set, not access denied. The fact that you get an access denied error on a sys object in the resource database indicates that the code signing of the system resource database (mssqlsystemresource) is broken. Did you drop any of the '##' certificates from master? did you manually altered any object in the resource database?
Anyway, you have a what looks like a corrupted instance at this moment and I'd recommend you contact product support on how to get it back into a coherent state.