We have solved a similar problem on our exchange servers (2 servers with the 
same problem). Running Legato Networker backup. Fullbackup ok, but incremental 
fails.

Error log:
MSEXCH: [5360] [I] 06/06/07 17:58:51 Opening connection to NetWorker Server...
MSEXCH: [5360] [I] 06/06/07 17:58:51 Processing storage group "First Storage 
Group"
MSEXCH: [5360] [I] 06/06/07 17:58:52 Backup storage group First Storage Group 
to Legato_bcp
MSEXCH: [5360] [E] 06/06/07 17:58:52 HrESEBackupGetLogAndPatchFiles: unknown 
error -939523534 (0xc8000232) (0xc8000232)
MSEXCH: [5360] [E] 06/06/07 17:58:52 Exchange ESE HResult: -939523534 
(0xc8000232); last error: 0 (0x00000000)
MSEXCH: [5360] [E] 06/06/07 17:58:52 The backup of First Storage Group failed; 
status is 0xc8000232.
MSEXCH: [5360] [I] 06/06/07 17:58:52 Completed backup of First Storage Group 
Status: 0xc8000232
MSEXCH: unknown error -939523534 (0xc8000232)
MSEXCH: [5360] [E] 06/06/07 17:58:52 Backup operation finished with errors. No 
savetime was sent.

Solution:
It seems to be something wrong with the public folder databases. Running 
eseutil /d pub1.edb (defragmentation) and then eseutil /p pub1.edb (repair) 
solved the problem. Note: The public folder database has to be dismounted 
during this process.

+----------------------------------------------------------------------
|This was sent by tebakken AT gmail DOT com via Backup Central.
|Forward SPAM to abuse AT backupcentral DOT com.
+----------------------------------------------------------------------

To sign off this list, send email to listserv AT listserv.temple DOT edu and 
type "signoff networker" in the body of the email. Please write to 
networker-request AT listserv.temple DOT edu if you have any problems with this 
list. You can access the archives at 
http://listserv.temple.edu/archives/networker.html or
via RSS at http://listserv.temple.edu/cgi-bin/wa?RSS&L=NETWORKER