I am trying to recreate a simple electronic part in Solidworks.  I got the IGES model from Digi-Key, but I need to modify it so the leads are poking through the circuit board housing. I tried sketching the geometry on a face and then extruding the housing from that sketch, but when I delete the imported model I get errors saying "This sketch contains dimensions or relations to model geometry which no longer exists."  If I delete all the dependencies on the original geometry then it tells me, "Could not find face or plane."  How do I get around this?