Error when uploading

I'm getting the following error when trying to upload to my arduino Uno. I am on windows Vista. It was working earlier but now I am getting this error. Does anybody know how to fix this?

Binary sketch size: 1228 bytes (of a 32256 byte maximum)
avrdude: stk500_getsync(): not in sync: resp=0x30
avrdude: stk500_disable(): protocol error, expect=0x14, resp=0x51

The Verbose outout info is:

Binary sketch size: 1228 bytes (of a 32256 byte maximum)
C:\Program Files\arduino-0022\hardware/tools/avr/bin/avrdude -CC:\Program Files\arduino-0022\hardware/tools/avr/etc/avrdude.conf -v -v -v -v -patmega328p -cstk500v1 -P\\.\COM3 -b115200 -D -Uflash:w:C:\Users\Ann\AppData\Local\Temp\build2134343747148350606.tmp\sketch_dec01a.cpp.hex:i 

avrdude: Version 5.4-arduino, compiled on Oct 11 2007 at 19:12:32
         Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/

         System wide configuration file is "C:\Program Files\arduino-0022\hardware/tools/avr/etc/avrdude.conf"

         Using Port            : \\.\COM3
         Using Programmer      : stk500v1
         Overriding Baud Rate  : 115200
avrdude: ser_open(): setting dtr
avrdude: Send: 0 [30]   [20] 
avrdude: Send: 0 [30]   [20] 
avrdude: Send: 0 [30]   [20] 
avrdude: Recv: 
avrdude: stk500_getsync(): not in sync: resp=0x30
avrdude: Send: Q [51]   [20] 
avrdude: Recv: 
avrdude: stk500_disable(): protocol error, expect=0x14, resp=0x51

avrdude done.  Thank you.

Did you read the troubleshooting guide? Did you do a loop-back test?

If not... do it now!