We just upgraded from 2003 to 2007. We have over 50 accounts and are using
exchange 2007 and only one person seems to be having this issue so far.
It is only with meeting requests, not emails. After you have entered all
information, and click send, an error is displayed and the To line is full of
semi colons and the names have dissappeared. the error appears in the event
log as source Outlook event number 25 but no information can be found related
to this error. "Could not complete the operation. One or more parameter
values are not valid."
I have tried recreating the group, creating new groups with different names,
diagnostics on Office 2007 and nothing seems to fix it.