IDE wont write to board

I've had my SB Freeduino for almost a month now and its worked fine until tonight. When I attempt to write a sketch to it it gives me this error:

avrdude: verification error, first mismatch at byte 0x0000
         0x0c != 0x00
avrdude: verification error; content mismatch

The last sketch that I wrote to it is still there and works fine.

Helo! I have the same problem whith my Arduino Duemilanove. I hope someone can help.