RE: The line distribution buffer record does not exist for ICN
check if there is a table with name "line distribution buffer" or "distribution buffer" in the old nav 5.1 database and if that table is missing in the new nav2013 r2 database. if yes, export it from the old database and import it to new database.
check also the nav object(s) - pages, report - , which use that table and show that error, if they are merged correctly.
it seems that this table is a customization provided by a nav partner. if so, best you contact that nav partner, could be serenic software.