Abit p35-e mobo problem.

Guys i am having problem with my abit p35-e mobo.Whenever i switch on pc from cold it gives me the following error msg:
C1E BIOS Supported EM64T CPU
Memory Frequency For DDR2 666(Single Channel Mode)
CMOS Checksum Error - Defaults Loaded

even if i save and exit bios setup with optimized default.Every time i start pc from cold it gives me same error.
I have tried flashing bios with latest version.Also i have changed the cmos battery,before this there was no such problem for almost 1.5 yrs...also pc is double booting every time....
and some times on turning pc on, every thing cpu fans, dvd drive, keyboard etc are running but pc does not boots even after many retry.

I am having intel E8400 3.0 GHZ processor, and my ram is 2Gb DDR2 800mhz but error is showing 666 mhz ram.

if pc is able to boot then after error,there is no problem .

Guys plz help
thanks in advance..

which bios?

bios verion:18

^^m using bios 18 and i dont face ny double boot issues. R u sure u using the same?.

yes i am using the same bios,as its shown by abit bios flash menu.
i have also searched on the net,the double boot is common and its like mobo self test.Before this problem i was also not having this double boot but now everytime mobo is double booting.Before the problem i was having bios version 14 but after the error and double booting issue ,i updated bios to 18 version but it didn't help.....

update......?

Try clearing CMOS,on the next boot,goto bios and make the required changes save.Reboot and see if it persists.