WD20EARS compatability with Thecus N4200

I bought a Thecus 4200 and 3 WD20EARS to go with it.  I have had nothing but trouble trying to configure a RAID 5.  Thecus now claims the EARS drive is not on its compatability list although the WD20EADS is on the list.  

As far as I know the only difference between the EADS and EARS is the size of the on board cache.  Is there (could there be) anything to Thecus’ claim my drives are not compatable?

The EARS drive is a 4K sector drive.  The EADS drive is a 512 sector drive.