elcapitan154 is right. there might be some trust issues with the custom ROM and your exchange server. I was having the same issues with the stock sprint 6.5 ROM and my works exchange server until I remembered I has an old copy of the cert on my palm pc. check out this post for instructions on how to obtain a cert when your phone will not pull it:
http://forum.ppcgeeks.com/showthread.php?t=117321