From here: https://dougieflash.wordpress.com/2013/03/08/updates-are-currently-disallowed-on-get-requests-to-allow-updates-on-a-get-set-the-allowunsafeupdates-property-on-spweb/

If you are in Central Administration > Manage Web Applications and go to the General settings option,
you might run into this error:

· “Updates are currently disallowed on GET requests.

· To allow updates on a GET, set the ‘AllowUnsafeUpdates’ property on SPWeb.

· Troubleshoot issues with Microsoft SharePoint Foundation.

Correlation ID: e845bd26-f70b-4f65-a023-82ca9d126031”

This error occurred in my dev environment. The behavior was that new applications would throw this error,

“Updates are currently disallowed on GET requests” under the General Settings. The error stack trace mentioned

‘EnsureHttpThrottleSettings’ so it means that CA is trying to update these setting on a GET request for new apps
that don’t already have them.

Resolution via Powershell

Launch Powershell and and add these lines:

$w = get-spwebapplication http://yourwebapplication
$w.HttpThrottleSettings
$w.Update()

The call to the HttpThrottleSettings ensures they exist and Update() saves them.

After completing these commands, you should be able to successfully launch the General Settings dialog window.