Go to Control Panel -> User Account -> Change User Account Control Settings.
If the lowest option (Never Notify) is selected, move up the slide to "Always Notify" or to the Windows recommended option (in bold), the one below "Always Notify."
Restart your computer and now the mobile devices sign in dialog should work.
Then, if you want, you can revert User Account Control Settings back to "Never Notify". But if you want disable UAC controls completely you must also:
- Change to 0 the registry value of "EnableLUA" in HKLM\Software\Microsoft\Windows\CurrentVersion\Policies\System;
2) Open Group Policy Editor (gpedit.msc), expand Computer Configuration -> Windows Settings -> Security Settings -> Local Policies -> Security Options -> User Account Control, set to "Disabled" the policy "Run all administrators in Admin Approval Mode" and restart the pc.