WARNING: [302-21-147-80020009] Unable to migrate message ‘ blah blah ‘ in folder '~CALENDAR'  Exception occurred. Description: Document does not exist (1825)
This may be caused by data corruption or a delay in the connection to the Groupwise server during migration.
Run GWCHECK several times prior to the migration as per SOL59640
If you need the migration to proceed past this type of error rather than fail out, try setting the Inactivity timer to 0 as per the GME_INI_Reference.pdf, this will prevent the migration from retrying these types of problem messages and potentially crashing the migration.
DoInactivityTimer=<#> .......................................... boolean ..... 1
Determines whether the batch-migrator program's inactivity timer is enabled or
disabled. For example:
… tells the program to abort a process if it receives no response from the
destination server for longer than a specified number of minutes following a data
transmission. The timeout limit is 40 minutes by default, or you can specify
some other value by the InactivityTimeoutMinutes= parameter (also in this
[General] section). To disable this feature, set DoInactivityTimer=0.