Combo selection is not set by class

Dropdown value is not set when using the following code (for trigger concept)
but the same code works fine for text entries.
This code dynamically set the values based upon some triggers.
TMFileManager.SetValue PROCEDURE( SHORT intField, STRING strValue )
sv ANY
Idx LONG
CODE
sv &= WHAT(SELF.Buffer, SELF.GetFileNo(intField))
IF ~sv &= NULL
sv = strValue //issue with dropdown but works with entry controls.
.
.
RETURN