To disable single router mode, do the following configuration.
Go to the desginated router, enter the following commands...
Router(config)#redundancy
Router(config-r)#high-availability
Router(config-r-ha)#no single-router-mode
Then after, do "wr mem" on both designated router and non-designated routers. And ensure that in non-designated router conf also, the "single-router-mode" not exists. Then, do reload.
Refer this doc for more info....
http://www.cisco.com/univercd/cc/td/doc/product/lan/cat6000/sw_6_3/confg_gd/redund.htm#11134