Tell us the account you want to use to open _vti_rpc.

I also get it on PowerPoint.

With Word and Excel, I can "X" out of the dialog and move on.

With PowerPoint, it just freezes and I have to kill the whole process in Task Manager :(:(:(

I'm on build 1607 and still getting this problem.  It only affects Word and Excel.

Its been happening now for at least 5-6 weeks.

How can you go back to the previous version of Office?

The reply from this thread (also mentioned here) about deleting your cached credentials solved the dialog box problem, but now I have a much worse problem. Now every time I open a document for the first time since the update that introduced the _vti_rpc dialog box, Word hangs and I have to kill the process. Second time I open the doc it's fine, but for someone who works with Word docs all day long, this has crippled my productivity.

So consider how annoying it is to X out of the authentication prompt (which is harmless) vs. how annoying it would be to have Word hang every time you open a doc for the first time. If you mostly work with the same docs over and over, it might be worth doing the above solution.

This solved the dialog problem but now Word hangs every time I open a document the first time, new or old. :(