If you install Exchange 2013 CU1 in an existing Exchange 2010 SP3 environment you might wonder why you will be redirected to Exchange 2010′s OWA/ECP when trying to open Exchange 2013 EAC.
In a mixed environment you have to add the Exchange client version as parameter:
https://yourEXCHANGE2013-CASServer.yourdomain.com/ecp?ExchClientVer=15
After adding this parameter you should be able to open the EAC.
Cheers, Chris
