When creating viod form it show "Can't keep elements joined" in particular part of family

[aksarakmal1]

In this family I want to make expansion joint, so I created void, it cuts some part but not all place.

[RDAOU]

@aksarakmal1 

The error/warning prompt you are getting could be due to several reasons. The thing is, it is hard to guess which applies in your case because it is hard to tell what you are trying to model, how you are modeling it and how do you expect it to look like when it is finished!