I would like to prevent a test case "Execution Status" in test plan from being updated, when the test is executed in a test set in Test Lab (for instance, in the example below, when the qc user is "toto")

I tried the workflow code below under the Test Plan Module script section, but the Test_FieldCanChange() event doesn't seem to be triggered. Is it only trigerred when I am in the Test Plan view of QC? If so how can get around that?

Function Test_FieldCanChange(FieldName, NewValue)
On Error Resume Next
If User.UserName = "toto" and FieldName = "TS_EXEC_STATUS" Then
Test_FieldCanChange = False
End If
On Error GoTo 0
End Function