I too was seeing this very frustrating error. Since making the below change though it appears that the problem is resolved.
Note that I am not running any of the programs (Bing Desktop etc.) that are commonly attributed to this issue, even by Microsoft themselves.
It seems this might be caused by the Office Clipboard, the need for which I have never been quite sure of since it appeared in Office many years ago. Turning off the notification or recognition for Office Clipboard seems to do the trick.
Open up the clipboard options by clicking the expansion arrow on the ribbon in the home section (this is Excel, but other Office apps should be identical or very similar).
Open the Options dialog at the bottom left of the pane that opens up. Select 'Collect Without Showing Office Clipboard' and close the pane.
Hopefully the issue is now resolved and you can copy and paste without errors or the cell focus being lost.
Edit: It appears, anecdotally at least, that this may be related to running the 32-bit version of Office on a 64-bit OS. That's certainly what I'm doing and many others seems to be in the same situation. Be interesting to see if this holds true.