AppleShare IP Migration Utility borking on mail data

Hi all, Attempting to move a bunch of mail (1.8 Gb and 50 users) from ASIP 6.3 to OS X Server 10.3.4 and I can get the users across mostly (nothing I can't fix with judicious use of Perl and a large hammer) but the migration utility totally refuses to even touch the mail database. It does nothing and logs nothing. Anyone had a similar problem? I've checked that the database is OK using the ASIP tools, I've checked it from the ASIP mail server. Tony Williams