Convert Nav 2009R2 to Nav 2013

Hello everybody,
Following the microsoft blog about upgrading (from Nav Database 2009R2 to 2015) and When trying to open Nav Database 2009R2 with DynamicsNav 2013 i get the following error.
Can't drop table "$Item Ledger Entry" because it is referenced by the object "$Item Ledger Entry$VSIFT$7".

Any suggestion to this problem will be really appreciated!

Thank you.