Anyone know how to get around this error?

I assume it is because "thickness" is a system defined global variable, used for sheet metal. This is exactly what I want. There is an old hack (in previous versions of SolidWorks), where if you define "thickness" once, it then always brings up the option to tie the thickness of any extude to the thickness variable.

Is there a new work-around in more recent versions of SolidWorks? I haven't tried to do this in quite a while.