Perhaps you are accidentally creating another cast member
with the same name, at an earlier position in the cast. When you
specify a cast member by name, it will always find the first cast
member with that name.
Eg, you have a text member called "qrs" as cast member 5.
Then you create a bitmap member also called "qrs" as cast member 1.
This will trigger the error you describe as the director will
always find the first cast member (the bitmap one).