The problem with the dapper->hardy upgrade calculation is that libnfsidmap1 has priority "standard" while libnfsidmap2 has priority "optinal". That makes apt prefer the former one over the later one and that breaks the upgrade.
The problem with the dapper->hardy upgrade calculation is that libnfsidmap1 has priority "standard" while libnfsidmap2 has priority "optinal". That makes apt prefer the former one over the later one and that breaks the upgrade.