Take a look at emc60614. I fixed same problem on CX3 box after vault HDDs replacement.
Hi every body   I'm new to EMC tech. so I started a testing environment using two cx3-20, the first one is working fine with no alerts or errors, the other cx3-20 i build from scratch (2_SP, 2_SPS, DAE3p) I checked there compatibility with cx3-20 and it came OK, so the Q. is :  the DAE that I used with the new system had now drives so when I mirrored the vault disks from the old system I encountered a problem with the write caching being disabled. I tried every thing with no luck at all ( flare V. 3.26.020.5.32 latest )
(7bd) Write Cache Enable Pending. Vault LUN not enabled or not valid.[0x00] 
ffffffff 4