When converting a 2.x board to 3.0.8, if the 3.x board is installed using MSSQLNATIVE (MS-SQL 2005+ Native) the converter will reliably throw fatal errors. The first error is: "cannot insert into pk_forum_id when IDENTITY_INSERT is set to OFF", if you enable identity insert manually on that key the next error which cannot be worked around is "cannot truncate table 'phpbb_userconv' because it cannot be found or you do not have permission" (the table is never created).

An effective workaround is to use mssql_odbc when installing the 3.x board.