OK here is how to un-associate a file extension to unknown . . . Right click your Desktop, choose 'New' - Text Document When the document opens, you need to save the document with a .bat file extension Click File - Save As At the bottom of the save as dialog, change 'Save as Type' to 'All Files' Manually enter the file name XXX.bat Now right click any file you want to disassociate and choose 'Open with' - 'Choose another app' -' More Apps' Check the box marked 'Always use this app' Scroll to the bottom and click 'Look for another app on this PC' Navigate to the XXX.bat on your Desktop and select that Finally delete XXX.bat from your Desktop and restart your system The file association will be reset to unknown . . .
If this happens then check the Application Event Log. If you see the message below then you need to change your registr settings
MAPISendMail: Failed to submit message. Attachments to the message exceeded the size limit set by your Administrator.
Computer\HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Preferences
If there is a Key called MaxiumAttachmentSize then delete it or enter a value of 1000+. Setting it to zero appears to cause this error.
Helpfull link: https://support.microsoft.com/en-ca/help/2813269/attachment-size-exceeds-the-allowable-limit-error-when-you-add-a-large
From: http://windowsitpro.com/windows-server-2016/q-edge-can-t-be-opened-using-built-administrator-account
Q: I recently installed the Windows Server 2016 Tech Preview and when I went to use the new Edge browser to go the Internet I got the following message. “Microsoft Edge can’t be opened using the Built-in Administrator account. Sign in with a different account and try again.” Does Edge now have something like Internet Explorer’s Enhanced Security? This is a test system and I don’t want to bother making multiple accounts. How can I get my Windows Server 2016 test system connected to the Internet when I’m running as Administrator?
A: Fortunately Edge doesn’t have anything like the annoying Internet Explorer Enhanced Security. However, Microsoft has made Edge more like a true app and they have enhanced its security to restrict browsing for highly privileged accounts like the local administrator. There are a couple of workarounds. The simplest is just to use Internet Explorer (IE). IE is still present in Windows Server 2016 and you can start it by opening the Start menu and clicking on the Internet Explorer tile. IE security is still controlled by Internet Explorer Enhanced Security and it won’t display that error message.
Alternatively, if you want to use Edge you can change to the local security policies to allow Edge to run under the Administrator’s account. Use the search option in the taskbar and enter secpol.msc then click on it in the search results. Under Local Policies, Security Options navigate to User Account Control Admin Approval Mode for the Built-in Administrator account click on it to open the properties. Set the policy to Enabled and click Apply. After you reboot the system you will be able to use Edge under the local Administrator account.