Server cannot modify cookies after HTTP headers have been sent (RoleManagerModule.OnLeave)

Over the weekend we had to upgrade the server's version of ASP.Net AJAX which went fine until this morning when we started receiving the error "Server cannot modify cookies after HTTP headers have been sent."

Luckily this wasn't bubbled up to the UI but incase other people are getting the error I thought I would share the fix. The error is apparently a known error with ASP.Net AJAX and the RolesManager. To fix the error all you need to do is add the following to your RolesManager web.config node:

cacheRolesInCookie="false"

The full error message was

Message:
Server cannot modify cookies after HTTP headers have been sent.

StackTrace:
at System.Web.HttpCookieCollection.Add(HttpCookie cookie)
at System.Web.Security.RoleManagerModule.OnLeave(Object source, EventArgs eventArgs)
at System.Web.HttpApplication.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)