Migappworker hangs during each migration run (4313786)

When migrating mailbox data migappworker hangs a few times during each migration run.
This kind of event is in the eventlog:

Reporting queued error: faulting application migappworker.exe, version 4.1.1.18, faulting module nnotes.dll, version 7.0.20.6269, fault address 0x00001457.

This can be cause by an issue with the Notes Client

Check for an error in the crashdump-files in the C:\Program Files\lotus\notes\data\IBM_TECHNICAL_SUPPORT path.

The error is:

PANIC: Invalid pool free chain

This ibm-article describes the problem and a solution.
http://www-1.ibm.com/support/docview.wss?fdoc=wplcdomi&rs=463&uid=swg21266629

Upgrading to Notes client 7.0.3 and rerunning the batch migration should fix the issue.