I’ve been getting what I thought was distributed cache errors on my SharePoint site. If I try and open a dialog box to add an image or document to a content webpart, its blank. This only happens on the top level site and not on a subsite that inherits the masterpage, pagelayout and permissions. To me that simply wasnt logical for my little mind! So a very long search led me to believe its distributed cache. I thought that multiple calls to files on page load such as css and javascript files failing and giving me 401 errors was causing by this, so I conceeded an appFabric update was required. I used a couple of sites as I was fully aware of the problems doing it wrong would cause.
Now although appFabric needed upgrading, and to be fair, its now a skillset I’ve acquired, its not the cause. That I still havent sorted yet! But I have discovered why there’s multiple calls and 401 errors.
As this link states, its due to NTLM, something we have running. First call is an anonymous call and really a 401 error is expected. Next call is a NTML call as the first one says do that next and expects a 401 first as its a challenge request, then you should get a 200 code. All expected behaviour apparently.
So the issue I started with persists but I now know why a double 401 error happens and also how to update appFabric the correct and safe way. Even if I did have an issue halve way through, a solution was found below in order to correct and restart it.
http://almondlabs.com/blog/manage-the-distributed-cache/
