We are using Mantis in version 1.2.11 with inheritable versions and categories.

I've experienced a number of issues during migration to remine.

First I had to modify the script a bit, to be able to migrate from our Mantis version (some small schema changes).
Second I had to find out, why a bunch of bugs from Mantis were not migrated to the redmine.

Thanks to Aaron Schroeder I've got some ideas where to search for reasons [[[http://www.redmine.org/boards/2/topics/41796]]].

Then I've modified the script to preserve project inheritance, to take over the inheritable versions, inheritable categories and versions closed status.

After all I've decided to add due_date to the redmine issues automatically based on the the last modification of the closed mantis bugs, because we haven't used due_date in mantis at all.

The Mantis knows three version fields (version, target_version and fixed_in_version) and I've modified the migration script to consider both fixed_in_version and target_version (to take the target_version if fixed_in_version is not set).

To be able to use inheritable categories I've applied a slightly modified patch #11898 to the 2.5-stable branch of redmine.
I've tried to modify the migration script to take over the inheritable categories in the way, that if you haven't applied a patch for inheritable categories, then the script should works as if it hasn't considered inheritable categories, but I haven't tested it appropriately.

I had to change a migration script to stay on the last failed saving of the issue and to output the occured errors to be able to find a reason of the failure. But I've reverted a change in the patch to not irritate an unexperienced users.
If I'll find a time to implement error logging in a smart way, then I'll add an updated patch to this post.

So here is my patch to the migration script: