Exchange log on and transaction errors.

We are experiencing errors on our exchange server.

Note: there are many of the 1022 errors for various users throughout the organization.  The 9791 errors show up intermittently as do the 623 errors.  The errors began today around 2pm and are continuous until now (4pm).  Users are getting error messages in their mailboxes and Outlook client performance is very slow to unresponsive at times causing some to have to restart their Outlook application to full reboots of their desktops.

What might the issue be??



Event Type:      Error
Event Source:      ESE
Event Category:      Transaction Manager
Event ID:      623
Date:            4/5/2012
Time:            3:31:01 PM
User:            N/A
Computer:      <Server Name>
Description:
Information Store (4520) First Storage Group: The version store for this instance (0) has reached its maximum size of 155Mb. It is likely that a long-running transaction is preventing cleanup of the version store and causing it to build up in size. Updates will be rejected until the long-running transaction has been completely committed or rolled back.
Possible long-running transaction:
      SessionId: 0xBD534080
      Session-context: 0x00000000
      Session-context ThreadId: 0x0000169C
      Cleanup: 1

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Event Type:      Error
Event Source:      MSExchangeIS Mailbox Store
Event Category:      Logons
Event ID:      1022
Date:            4/5/2012
Time:            3:31:08 PM
User:            N/A
Computer:      <Server Name>
Description:
Logon Failure on database "First Storage Group\Mailbox Store (<Server Name>)" - Windows 2000 account <account name> ; mailbox /o=< sanitized> ou=Administration/cn=Recipients/cn=< sanitized> .
Error: -1069

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Event Type:      Error
Event Source:      MSExchangeIS Mailbox Store
Event Category:      Logons
Event ID:      1022
Date:            4/5/2012
Time:            3:31:18 PM
User:            N/A
Computer:      < sanitized>
Description:
Logon Failure on database "First Storage Group\Mailbox Store (< sanitized> )" - Windows 2000 account < sanitized> ; mailbox /o=< sanitized> /ou=Administration/cn=Recipients/cn=< sanitized>
Error: -1069

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Event Type:      Warning
Event Source:      MSExchangeIS Mailbox Store
Event Category:      Background Cleanup
Event ID:      9791
Date:            4/5/2012
Time:            3:31:19 PM
User:            N/A
Computer:      < sanitized>
Description:
Cleanup of the DeliveredTo table for database 'First Storage Group\Mailbox Store (< sanitized> )' was pre-empted because the database engine's version store was growing too large. 0 entries were purged.

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