WAX620 Clients Cannot Obtain IP Address

Hi, I have four WAX620s hosting two SSIDs.  Randomly and very frequently clients can connect but cannot obtain IP addresses (message looks like: BREAKROOM: 56:33:86:b6:a6:42 could not obtain IP address on COG-GUEST).  There are two VLANS, one assigned to each SSID.  DHCP is working fine and there are plenty of addresses available.  There are no DHCP requests showing on the router, unless the connection is successful.  The problem exists in both BRIDGE and NAT modes.  The problem seems to be getting worse with time.

Also, clients that are connected frequently get disassociated and reassociate a couple of seconds later.  Over and over again.  Eventually they won't be able to get an IP address.

Has anybody had any similar experiences?