Arduino upload errors

I recently tried to upload my sketch after adding one output pin. The sketch compiles ok, but will not upload. I get the following text after trying to upload.

avrdude: stk500_paged_write(): protocol error, expect=0x14, resp=0x64
avrdude: stk500_cmd(): programmer is out of sync

I've tried several times with different sketches and have also gotten the following message;

avrdude: stk500_paged_write(): protocol error, expect=0x14, resp=0x64
avrdude: verification error, first mismatch at byte 0x0080
0x02 != 0x58
avrdude: verification error; content mismatch

I would greatly appreciate any help interpreting the error messages. I can't load anything to my Arduino Duemilanove w/ATmega 328. I'm using the latest Arduino 1.0