Combo Dropdown selection is not set by class

Combo 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

    sv &= WHAT(SELF.Buffer, SELF.GetFileNo(intField))
    IF ~sv &= NULL
      sv = strValue //issue with dropdown but works with entry controls.