I ended up finding the resolution by nosing through the database schema at Ravenbrook. It fixed my problem but I'll post the fix here in case anyone has a similar problem.
The problem lay that in the new version, in the "bug_status" table there is a new column called "is_open". When the old database was converted it added a "1" to each row. This needed to be changed to "0" for all bugs considered closed ("Resolved", "Verified" and "Closed"). Once this was changed, the resolution drop-down menu appeared and was populated with the list of resolutions. This also resolved the issue with the Sanity Check error messages.
For reference, the schema I used was;
http://www.ravenbrook.com/project/p4...-bug_status-id