Don't worry about the error - that simply means that it was unable to save the backup files it creates.
Here's my usual instructions post for the MGADiag report....
To properly analyse and solve problems with Activation and Validation, we need to see a full copy of the report produced by the MGADiag tool
(download and save to desktop - http://go.microsoft.com/fwlink/?linkid=52012
Once saved, run the tool.
Click on the Continue button, which will produce the report.
To copy the report to your response, click on the Copy button in the tool (ignore any error messages at this point), and then paste (using either r-click/Paste, or Ctrl+V ) into your response.
(please enclose the report in 'CODE'using the options in the response - this makes the threadeasier to read)
Please also state the Version and Edition of Windows quoted on your COA sticker (if you have one) on the case of your machine (or inside the battery compartment), but do NOT quote the Key on the sticker! http://www.microsoft.com/en-us/howtotell/Hardware.aspx