The problem could be because you cannot Set Focus on a Form if it has one or more Controls that can have data Added/Edited. To move to a Subform , via code, you have to Set Focus to the Subform Control on the Main Form...which may or may not have the same name as the name of the Form the Subform is based on.
The Form your Subform is based on apparently is sfrm_Label_Tracking...but is that the name of the Subform Control it resides in?
Linq
The problem with making anything foolproof...is that fools are so darn ingenious!
All posts/responses based on Access 2003/2007