Your post says that you imported users into exchange and I just want to confirm that is the case, and you didn't mean "after importing users from exchange into Unity." However, if you did import users into exchange, try taking the account that you were originally able to access the SA with: Go into Exchange admin, chose the user and under "primary windows NT account" re-select the account. Log off, and log back on to the server and see if you can access it. You can also try associating the user with a different account, then associating back to the correct one.
Will
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Will Roach
Systems Engineer
Cisco Systems, Seattle - TAC