Free/Busy not working Exchange 2007 and 2013 co-existence

Hi,

I'm migrating our Exchange 2007 environment to Exchange 2013. Now I am in a co-existence environment where all the mailboxes except some test-users resides on Exchange 2007. Between Users on the same Exchange MBX Server athe FREE/BUSY Information sharing works correctly, but between Exchange 2007 and 2013 it's not working.

I verified my settings and also the EWS virtual directory on 2007 CAS Servers using Get-WebServicesVirtualDirectory. The internal and the external URLs are set to https://legacy.mydomain.com/....

What am I missing?

Thanks & Kind Regards,

Jürgen