APPLICATION.setVariableValue - BEx variable configuration

Hi

I want to use the function APPLICATION.setVariableValue() or APPLICATION.setVariableValueExt() in the "On Startup" area to pass a java script variable to a BEx variable. No mather how I configure the BEx variable I get the error message "Value "ZTEST_DELETE3" is not a valid variable" (BEx variable name is ZTEST_DELETE3). Design Studio 1.2 "sees" the BEx variable since I am able to choose it from the content assistant.

How do I need to configure the BEx variable for Design Studio 1.2 approve the variable.  

Kind regards

Erik