This error is the bane of my existence. It occurs when absolutely NOTHING has been erased. "CHANGE_LOST_ENT: attempt to change record marked as deleted" After this occurs, it seems as if fairly nothing will ever again work in the part, and you nearly always have to just go back to a prior save, or abandon the part and re-create it in its entirety from scratch. Is there any way to recover from it? I know this is an impossible question, as you don't have the part, but I can promise you that you would be no smarter if you DID, as there is never any information given as to what the "lost entity" is. This is an ACIS error, and simply has no explanation other than what one can guess. Sometimes one can undo or get rid of the last few items in the design explorer and it will work, but other times the lost entity remains forever a mystery until you lose the entire this by just deleting and starting over from scratch. I'd REALLY like to know what these ACIS errors are referring to, but I am afraid that even if the reference is given it would just be the GMD internal descriptor, and would mean nothing to the user.