Hi Varun, if I understand what u are trying to do, I’d say stop cutting and pasting! That only preserves what you see during the cut, if I recall.
So, for a 28,000 activities schedule, that should be a master plan that imbeds a subproject of 19,000 activities stored in another file. 9,000 activities are in the Master Project, and 19,000 are in the Sub Project, just to be clear.
I wrote up the detailed cut and paste procedure once… but alas, it was a different time 🙂 But its not hard, starting with the original plan, dup that, cut them up in the correct proportions, then imbed the sub into the master – done!