I have an unrooted g1 on firmware 1.0 and RC29. I am trying to manually update to 1.5 cupcake but does not seem to work. I have tried to manually update to all the firmware updates and get the same error every time when in recovery mode. After typing ALT L then ALT S, error message says,

E: no signature
E: verification failed

then installation aborts. I know its not a bad update I am downloading because I have tried them all even 1.6 donut. I have done a lot of research and have not been able to find any answers. So I am asking if anyone out there can help me, please do, Thanks. My email is raidersway_510@hotmail.com feel free to email me any time.