Currently where are migrating our exchange to Exchange 2007. One secreatary send the invitation meeting to CEO and she received the email that meeting was accepted. However it was sent by BESAdmin on behalf of CEO. We are using BB Enterprise server 4.1.16Please help

BesAdmin is the service that deals with meeting requests.The CEO has accepted the meeting via his blackberry so the BES server had to deal with the transfer of the meeting acceptance, hence why you are seeing the message 'BESAdmin on behalf of CEO'.There maybe an option to change it on the BES Server, the same happens here with ours. Never seen it as a problem, after all the BES Server is the link between the blackberries and Exchange.Hope it helps.

Sounds like your BESAdmin account has Send on Behalf instead of Send As permisions. Changing the accounts access will solve your issue.Both RIM and MS recommend using Send As.

I had follow this documentation: http://www.blackberry.com/btsc/viewContent.do?externalId=KB02276during upgrading the BES server. After did it, i did check on user mailbox permission and result is BESadmin has full access right while on Send AS permission, BESAdmin didn't have permission. Some one from blackberry forum had provided me the documentation and after follow his link, now BES had "Send AS" permission.