There appears to be an issue with the new MultiProcess and SingleProcess open modes when opening an older format database.
I think you can work around it--after exiting and restarting Data Builder to make sure all file handles got closed--by going directly to Database -> Upgrade VDB5 or Older Database without opening the database first. It should also be avoided if you only open the older-format database in SharedReadOnly or ExclusiveReadOnly mode if you need to examine it first. (As of the 6.0 release, opening pre-6.0 databases is only allowed in a ReadOnly mode or when upgrading to the current format.)
Sunil Prasad
I just downloaded BistaDB6 and trying to Pack a VDB5 file and keep getting error message that file is locked by another user. I am using the data builder