'Group is too large to display. communicator can not be used for groups with more than 100 members

you might receive this message in OCS 2007 Client when you try to expand a group in OC.
first you have to know that OCS client is hard coded with a maximum of 150 members to display, if you want users to display more than the default 100 limit then create the following client side policy and restart the OCS Client:
Open Registry:
go to
HKLM\Software\Policies\Microsoft\Communicator.\
Create a Key: MaxDLExpansion (DWORD)
and type 150 as the value.
More KBs:
http://support.microsoft.com/kb/945542
http://social.technet.microsoft.com/Forums/en/ocsaddressbook/thread/09a20c42-0e04-4f64-9aa7-dc3f1f4a1cd4
Thanks to Jeff for that great hint