Hi,
Thank you for posting your query on Microsoft Community.
As per the description, I understand that you are facing issues with using media creation tool.
This might have occurred whether it is not installed properly or may be due to some third party application conflicts.
I would suggest you to again download the windows installation media creation tool again and check if you are facing the same issue.
For more information you can refer to the below link:
http://windows.microsoft.com/en-US/windows-8/create-reset-refresh-media
If issue persist, then download Windows 8.1 ISO or create media.
Follow the link below to create media:
http://windows.microsoft.com/en-US/windows-8/create-reset-refresh-media
Before downloading the tool I would suggest you to temporarily disable the antivirus security software program installed on your computer and check.
Disclaimer: Antivirus software helps protecting your computer against viruses and other security threats. In most cases, you shouldn't disable your antivirus software. If you have to temporarily disable it to install other software and\or troubleshoot any pertinent issue, you should re-enable it as soon as you're done. If you are connected to the Internet or a network while your antivirus software is disabled, your computer is vulnerable to malware attacks.
Hope this helps. Please let us know the results. We will be glad to assist you further.