Arduino IDE Error

I am trying to use a Duemilanove on Windows 7. I am using one of the example sketches that comes with the program. Whenever I try to upload I get this error:

Binary sketch size: 1978 bytes (of a 30720 byte maximum) avrdude: stk500_getsync(): not in sync: resp=0x00 avrdude: stk500_disable(): protocol error, expect=0x14, resp=0x51

I have uploaded to this board in the past. It usually works flawlessly. But the serial port of the board is COM1, which is always available even if the board is disconnected. This may signal a driver issue. The is nothing connected to the board, and I have tried two different boards of the same model. Please help!!!

in the tools menu you can select the board-type used: UNO 2009 etc. Check if this setting is still correct,

When I switch between boards I sometimes forget to change it and AVRdude starts to "spit" similar error msgs.