MSExchangeSA 9320 Offline address book error

I have been troubleshooting some event log errors over the last few days trying to ID the issues.

I initially received the following error
Event Type:      Warning
Event Source:      MSExchangeSA
Event Category:      OAL Generator
Event ID:      9320
Date:            07/09/2010
Time:            05:02:44
User:            N/A
Computer:      SVR-Name
Description:
OALGen could not generate full details for some entries in the offline address list for address list '\Global Address List'.  To see which entries are affected, event logging for the offline address list generator must be set to at least medium.
- Default Offline Address List

Following that i received
9115 -OALGen successfully generated the changes.oab file
9347 - OALGen is building the offline address list index files of address list '\Global Address List'
9115 - OALGen successfully generated the changes.oab

Then another Warning
Event Type:      Warning
Event Source:      MSExchangeSA
Event Category:      OAL Generator
Event ID:      9323
Date:            07/09/2010
Time:            05:02:40
User:            N/A
Computer:      Svr-Name
Description:
Entry 'Administrator' has invalid or expired e-mail certificates.  These certificates will not be included in the offline address list for '\Global Address List'.  
- Default Offline Address List

Then the follwing confirmations
9346 - OALGen is building the offline address list index files
9117 - OALGen successfully opened a connection to Active Directory
9343 - OALGen will use 'C:\WINDOWS\TEMP\
9106 - Offline address list generation started.
9108 - Offline address list generation started.

After turning the logging up to medium it is showing the additional infomation (successes) above but not detailing what the issue could be.

Do you have any ideas?
Thanks in advance,