If you run into the error 0x80070721 there are a few things you can do.

1) Simply reboot. If this error just popped up for the first time it is possible that COM on the target computer needs to be restarted.

2) If the error consistently happens on a particular target refer to this entry on Microsoft's MSDN blog site.

3) Allow the computer to be trusted for delegation. Refer to this article on Microsoft's Technet site.