Mail target agent log shows Error 5116 Invalid value of attribute 'msExchMailboxGUID'. (4305213)

The following error is shown in the mail target agent log file:

21.05.2012 11:32:17 CADQueue::NextItem Informational 4511 Starting to process item '/O=test/OU=NL_HH/cn=Recipients/cn=test' (Collection 'nL22-11', PST: '7E2DA5E9ED5972489E6E0FD6F5257FB4', SyncMailboxInfo: 'True', SyncSwitched: 'False', SyncAllContent: 'False', SyncFolderContent: 'False').
21.05.2012 11:32:18 EMWLDAP40::LDAPOperations::CreateMailboxLDAPInfo Error 5116 Invalid value of attribute 'msExchMailboxGUID'.