Error Uploading Blink - Diecimila - Windows

I am totally new to Arduino. I just received a Diecimila, hooked it up to my PC running Windows XP, followed the instructions to install the drivers, and attempted to upload the Blink example. I received the following error:

java.lang.NullPointerException

at processing.app.Serial.setDTR(Serial.java:480)

at processing.app.Uploader.flushSerialBuffer(Uploader.java:76)

at processing.app.AvrdudeUploader.uploadUsingPreferences(AvrdudeUploader.java:69)

at processing.app.Sketch.upload(Sketch.java:1699)

at processing.app.Sketch.exportApplet(Sketch.java:1761)

at processing.app.Editor$42.run(Editor.java:1955)

at java.awt.event.InvocationEvent.dispatch(Unknown Source)

at java.awt.EventQueue.dispatchEvent(Unknown Source)

at java.awt.EventDispatchThread.pumpOneEventForHierarchy(Unknown Source)

at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)

at java.awt.EventDispatchThread.pumpEvents(Unknown Source)

at java.awt.EventDispatchThread.pumpEvents(Unknown Source)

at java.awt.EventDispatchThread.run(Unknown Source)

The green power LED is on and the orange LED is blinking (this means at least the bootloader is working?). Is this a problem with the drivers? Some sort of settings on my computer? I'm sorry if this is something that has been posted on multiple times, but I couldn't find it in the forums or the troubleshooting page. Thanks in advance.

Did you select the right serial port from the Tools | Serial Port menu? You want the that corresponds to the "USB-to-serial" entry in the Windows Device Manager. Also, if the port number is greater than 10, you should reassign it to a lower port.

That was easy. Thanks a lot.

No problem. I really need to improve that error message.

I'm getting the same errors with my 2nd Diecimila. One works fine and runs Blink. If I unplug it from the USB and plug in the other and upload to I/O board I get the error dump. I can switch back to the first and it works fine so I don't think it's settings.

Well, I figured it out. It was the Serial port setting. Seems that when I unplug one board and plug in another the serial port assigned to the USB connector changes. I need to set it each time I plug in a board unless it is tied to a particular board in which case I need to know which board comes up as which port.

Is this normal under WinXP?

Windows changes port numbers again if you use different USB ports. But once you have defined a port number, to a specific Arduino board, plugged to a specific USB port, then you can switch Arduino boards and windows keeps the defined port number.