When importing memberships into 4.6.8, what does ""The membership cannot be saved because the status cannot be calculated" mean?
This error is part of CRM_Member_BAO_Membership.  It's triggered when there's no membership status that fits the dates in question, and so this error depends on the day you do an import!

For instance, if your memberships statuses are:
Start Date to End Date = Current
End Date to (End Date + 1 month) = Grace
(End Date + 1 Month) to Any = Expired

What happens if you import a membership with a start date of 10/25/2015 on 9/22/2015?  It's before the Start Date, so none of the statuses match.  This causes this error.

If you're getting this error and this is definitely not the case, replicate the problem on the demo server, you may have found a bug.