I've get the following error trying to delete at user from a security
list:

Could not find user with corresponding SID in the domain. Check the
spelling of the account name and try again.

I know that the users is no longer part of the AD, and are ind the
list: "missing in importet". But why can't I delete the users, that
no longer excist? What can I do?

Some where I read that I could go to:
http://servername/_layouts/1033/siteusrs.aspx

Here I get the following error:
Error executing child request for PortalHeader.aspx

Can anybody help?