Contacts showing as offline when I know they aren't!!!
 

I am using windows messenger 5.1 with SIP as my communications service in a
corporate office. I have 53 users that need to access this for
messaging/support etc... I have recently added new users and I am one of
them. Some if not most of my contacts are showing as offline when I know that
they are in fact online and not cloaking themselves (e.g. display as
offline). What can I do to make this work? Any help would be GREATLY
appreciated!