Error "execute permission denied" on a workflow

SYMPTOMS
When workflow is executed for an entity, it fails with an error message.
 
ERROR
Cannot find the object 'WFCALC_xyz', because it does not exist or you do not have permission.

Access to 'WFCALC_xyz' has been granted to CPACCESS and CHANGEPOINT, yet the system says that the permission is missing.
 
REASON
The GRANT statement has been included in the stored procedure because a GO statement is missing at the end of the code of the procedure definition. Thus SQL server tries to execute the GRANT statement every time the workflow is executed.

RESOLUTION
Add a 'GO' statement after the definition of the WFCALC procedure and before the grants like

CREATE PROCEDURE WFCALC_xyz
....
GO

GRANT EXECUTE ...
GO