I don’t understand how this should work. If you set AICC_Score to “” wouldn’t this mean not to send a score, i. e. remove a value that’s in it? Try to set AICC_Score equal to the test score, e.g. VAR(Test_1_Score). Just select the test score variable from the list.
Lectora would usually fill in the test score automatically, i.e. you don’t need an action to set AICC_Score. Check your test settings whether “Include test score in overall score” is checked. If it is checked you may try to just remove the action.