Fails to upload

[arduinoUser]

Everything was working fine until buying and plugging in a second arduino "Eleven" board for another project and now nothing uploads.

When I plug in the first board it is assigned COM8. If I unplug the first board and plug in the second board it is assigned to COM9.

Both boards now give this error:
====================================
Arduino: 1.6.6 (Windows 7), Board: "Arduino Duemilanove or Diecimila, ATmega328"

Sketch uses 1,030 bytes (3%) of program storage space. Maximum is 30,720 bytes.
Global variables use 9 bytes (0%) of dynamic memory, leaving 2,039 bytes for local variables. Maximum is 2,048 bytes.

avrdude: ser_open(): can't open device "\\.\COM8": The system cannot find the file specified.

The sketch blink was being used to test the boards.
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[andrew]

Please change the board type to Arduino Uno in the IDE's Tools menu and try again.

[arduinoUser]

@andrew,
Thank you for the quick reply. The first board is working again but when I unplug it and plug in the second board it fails.
It probably has something to do with windows giving the second board com9 instead of com8 but I don't know how to fix it.
Does each board have its own ID for windows to recognize as a different device?

error message:

Arduino: 1.6.6 (Windows 7), Board: "Arduino/Genuino Uno"

C:\Program Files\Arduino\hardware\tools\avr/bin/avr-ar: unable to rename 'core\core.a'; reason: File exists

exit status 1
Error compiling.

Sketch uses 1,030 bytes (3%) of program storage space. Maximum is 32,256 bytes.
Global variables use 9 bytes (0%) of dynamic memory, leaving 2,039 bytes for local variables. Maximum is 2,048 bytes.
avrdude: ser_open(): can't open device "\\.\COM8": The system cannot find the file specified.

[andrew]

If Windows is giving the second board a different COM: port value, you may need to update this in the IDE's Tools> Port... menu.
Please try that and see how you go.

[arduinoUser]

I couldn't actually edit the Tools/Port value but when I clicked the value shown something happened as it now appears to work. The first board is always assigned COM8 and the second board is always assigned COM9 so I assume the boards have an ID number that is recognized by Windows7. If I buy another board I assume it will be assigned COM10.

Still can't turn off the pop up library update request window that appears every time I do an upload to a board.
.

[andrew]

Windows allocates the COM: numbers, can be almost anything unused (e.g. I've seen COM23: last week).
You need up update the libraries to get rid of that message, or go back to an older version of the IDE.

[arduinoUser]

Ok. Where is the update button?
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