Test Plan Tree List

I am using this workflow  code for ALM 11.52  to allow the user defined list field to be populated with the subject tree list, however this is not working for me.

 


  Test_Fields.Field("TS_USER_01").List = Test_Fields.Field("TS_SUBJECT").List

 

 

 

However this code is flawlessly working fine in QC v 10. Do anyone know how to resolve this issue?. Could anyone share solution?. Aprreciate your help.