http://roundup.sourceforge.net/doc-1.0/admin_guide.html#migrating-backends

Please add the following to the 6th step:

6. use the roundup-admin "import" command to import the previous export with the new tracker home. If non-interactively:
roundup-admin -i <tracker home> import <tracker export dir>
If interactively, enter 'commit' before exitting.