I mean, it's a simple model (a one-family house), but it got painfully slow to do anything. It's saved locally on the computer I'm working on, so I guess it must be a problem with the model.
I fear however that I need to clean up the file itself too. I get now a message saying that the computer does not have enough memory for the operation (zooming in/out). It must be some corrupt element that I need to delete.
Is there a magic command like "get rid of all the stuff that doesn't work"?
Before merging them I would suggest cleaning up all the superfluous attributes with attribute manager in the corrupt file, and then merge them in a new file.