which is it cause the action derived not working?

Hi ,  i created a action  derived for the DdocTitle   but not working

in the field DdocTitle 

<$dprDerivedValue=#active.xSubTipoDocumental$>

the field #active.xSubTipoDocumental exists, and  modify the derived  with

<$dprDerivedValue="is my title$>, no working.

which is it possible cause?

my  version is 

Version:12.2.1.2.0-2016-10-06 07:41:00Z-r148019 (Build:7.3.5.186)

s

regards