i found the casue. not solution yet, tho.
i found out that when user gets message box 'outlook is retreiving data from exchange server <servername>", the data is retreived from global catalog server. (if the servername is FQDN) this is the part, i missed. so i checked the %processor time count on both global catalog servers in here, and bingo! one of them had constant high cpu usage (84-100%) and i think this was the cause of the pop-up message.
at earlier documents by MS, they said we'd have to contact ther support team but they just posted a new document:
this helped me see where the problem is.
now, my question has to jump to sql server since this global catalog server with high cpu usage is also a sql server.