When using the Test Repository menu to Add a Test to a Sub-Test Execution, an error is thrown by the system

Steps to reproduce:

• Create a Test
• Create a Sub-Test Execution 
• Navigate to the Test Repository
• Use the Repository Menu (right click) to add the Test to an Execution
• Select a Sub-Test Execution

Expected Result:  Test is added to the Sub-Test Execution

Actual Result: Error about the Test Plan limit is displayed.