partition can't be modified
Trying to upgrade to maverick. need to partition disc to do this, but error message says disc cannot be unmounted
MacBook Air, Mac OS X (10.7.5), trying to upgrade to maverick
If this is a disk with some data already on it, chances are that's why.
If this is a disk that hasn't been formatted for the Mac, it needs to be:
https://discussions.apple.com/docs/DOC-3003
Make sure your data is backed up before attempting any partition.
Also make sure your hardware requirements meet
https://discussions.apple.com/docs/DOC-3761
and