Are you trying to restore a V6.1 backup into a V8 instance as a migration procedure ... I'm not sure if this is supported ...
AFAIK, a migration using a backup is supported from a previous version (V6 to V7 ,V7 to V8 etc) is supported ...
Well, in any case, you will need a full offline image of the database ... A new version cannot rollforward through logs from a previos version ...
HTH
If not clear, pl ask
Sathyaram