Your database may be corrupt. Have you ran recover on the database to check for errors?
I use this calculation to extract a file name from a container field. Get ( activeFieldCOntents ) is not needed as long as I can refer to the container field directly by name:
This should work for all insertion and storage methods save Insert Object (FIleMaker 11, WIndows only):
Let ( [T = GetAsText ( GetValue ( YourTable::containerField ; ValueCount ( YourTable::containerField ) ) ) ;
L = Length ( T )];
Right ( T ; L - Position ( T ; "/" ; L ; -1 ) )