Change user's short name?

Hi and thank you in advance for any assistance you may give.

I am administering a group of computers for an office of about 20 architects. There is an XServe running 10.5.8 server. One user, when her server account was set up years ago had her name misspelled (Katie instead of Katy) on her server account. This has caused a few problems.

In an attempt to resolve them I went into the Workgroup Manager, changed her account's name and added a short name which included the correct spelling. The services she accesses are file sharing and calendar, she is running 10.7.4 on an iMac.

iCal, unfortunately, when I set her account to use the new short name, does not work and gives a 403 error. Setting the account to the previous short name works fine.

I do not seem to be able to delete the old incorrect short name from her profile on the server. Is there a way to do this, and will this allow the new short name to work in iCal? Will it cause other issues?

Any replies much appreciated.