unable to delete user mailbox

Hello,

I tried to delete username mailbox who is no longer with the company. His/her username still exist in the AD when try to delete the mailbox from Exchange I got the following error:

"error: Active Directory operation failed on servername.domain.local. This error is not retriable. Additional information: Access is denied. Active directory respoind: 00000005: SecErr: DSID-031520B2, problem 4003 (INSUFF_ACCESS_RIGHT), data 0.

CAn somone help me, please.

Thanks

Jimmy