The problem was cause by a Local Security Policy.
The fopllowing User Access Control (UAC) Policy setting was the problem:
Only elevate UIAccess applications that are installed in secure locations
The following article pointed me in the right direction.
For better, quicker answers on T-SQL questions, click on the following...
http://www.sqlservercentral.com/articles/Best+Practices/61537/
For better answers on performance questions, click on the following...
http://www.sqlservercentral.com/articles/SQLServerCentral/66909/