the International Rollei Club

I have recently aquired a rolleikin 2 set complete with counter knob, all alloy not black. I screwed the exposure counter knob to the body of a Rolleiflex 2.8 E2. However when attempting to close the back, the tab fixed to the back that prevents the original spool holder from being from being pulled out is catching the knob and the back will not close nor will the counter knob pull out. My question is ( after this long preamble ) do I need a different counter knob or a different back ? Does anyone have an answer, as I can find no reference to this issue in any literature I have been able to locate.
Thanks in advance.