Outlook Web Access problems

I was getting an error attempting to log into an exchange web mailbox with the message "The Local Security Authority can not be contacted". As it turned out this was actually due to the fact that the previous administrators had set this user up so that they were only allowed to logon from one particular workstation. I (thought I) had already solved this problem by adding the exchange server to the list of computers that the user was allowed to log onto but that didn't work - it was only after I removed the restrictions (which were not necessary now anyway) that they were able to get their mail via the web.