Well, for the failure you should run some debug to expand the error messages..

The "%s" usually happen when you install 5.1 module on Nw 7.3.x. That version of the module was designed to work with 7.4, which handle the logs in a different way (at least that's what I saw here sometime ago)

If scanner did not help, try to use 'nsrck -L7 -t ' and see if that helps. One thing Support had to do with one of my customers was to move the current index to a different location and start a new blank one for that client, then run scanner -i, do the restore, and move back the index. It's not a good solution, but was the only thing that worked (and they didn't tell why :D)

"%s" is not rendered log which is not normal if you run 5.1 against server which is not 7.4.x. To see it right you need to use nsr_render_log binary. If you server is 7.3SP3 based you will also need patch.

As for second problem, make sure you followed guide documented in release notes as getting back data in index has changed in steps required.