… and the copy/paste process starts working without an error, but is slow.
This comes up from time to time in the workbooks with corrupted styles: memory overallocation that impacts Excel workbook size. Here is a post with an answer:
Update [5/1/11]: the link above has been reported to “act up”. The full post is still available, you just need to scroll up. Here is recap just in case site owners decide to expire the post:
Check your used range/memory allocation in the workbooks that are still slow: hit END key (don’t hold it) and then hit HOME key on each worksheet. This action would take you to the last cell with allocated memory in the worksheet. If the row or column index is really high and you don’t have any data in the blank cells you have overallocated memory problem. Just delete blank rows and columns and save the file. The save process would reclaim memory back.