Error While Uploading

I had my arduino working great, a lot of succefully uploads, and programs, but the last time i tried to upload my new program, i started receive this error

avrdude: stk500_getsync(): not in sync: resp=0x30
avrdude: stk500_disable(): protocol error, expect=0x14, resp=0x51

Ive tried to upload the simple blink program to my Duemilanove, and i got the same error, i tried reseting after and before the upload, ...

i really dont know what to do, should i try to reflash the bootprogram? But how can i do it? Im aprentice in arduino, hope someone give me a light.

Thanks, cheers from brazil.

I too have this exact same problem. =(

Which board is selected?