backup problem on windows 7 home premium

hello friends i just want help
i am using sony vaio vpccw26 laptop,now i want to back up my window(c:drive)
when i m trying to back up using backup and restore tool ,it shows this error
{
the shadow copy could not be created,Please check "VSS" and "SPP" application event logs for more information
details:insufficient storage available to create either shadow copy storage file or other copy data
}
i have tried on my empty partition and other usb hard drive to take backup but it shows same error and ya i have more empty space than on c drive