Error message: "Unable to split wall panel(s)"

[lauraannegorden]

I keep getting the error message "Unable to split wall panel(s)" when I try to stretch or trim this one particular wall. This is an exterior "stacked" wall. I have no idea what the problem is and the error message does not elaborate.
Has anyone received this message before and is it solvable? I need this wall to trim.
Oh, and a 100% CD review set is going out tomorrow, so please help soon!
Thanks