Error: Updates are currently disallowed on GET requests. To allow updates on a GET, set the 'AllowUnsafeUpdates' property on SPWeb.

Solution:

To overcome from this error , set the 'AllowUnsafeUpdate' property of the SPWeb object to true.

Ex: SPWeb web = SPContext.Current.Web;
      web.AllowUnsafeUpdate = true;

Note: If we are working with web collection, we need to set this property to each web object.