How can I delete delegates.

[Tulsa Public Schools]

We have many users who need to read the calendar of others in the
organization. One of our two email servers crashed and had to be rebuilt. The
people who had delegate authority for folks in the latter part of the
alphabet now find that they can't open the calendars of folks who have
delegated Read authority to them. I have been able to add the same people
back to the folks who need to read the calendars but now they have two
listings for each person, one does not not work the new one does. How can I
delete the non working calendar reference? I can send a screen shot of the
problem.