I've got the same problem after upgrading from 4.8.0 to 4.11.10. Ben, could you elaborate a bit about your solution? What rewrite rule did you fix?

Hi Patrik,

This one was a while ago and if I remember rightly we had a rewrite rule which changed the casing for all URLs. The request URL was case sensitive so we removed that.

Hi Ben,

Thank's for your quick reply. Well I do not have that kind of URL rewriting, so I have to continue searching for a solution...
I'ts strange because it works on my local computer, but not on the server. 

Do you find the solution.. Its happening for us also on a 4.11.10 site.. 

There is no URL rewrites and the URL /base/FolderBrowserService/GetChildren/1160?_=1377115837768

shows <error>Extension not found or permission denied</error>

Yes, I finally found my problem. I had to change the IIS ASP.NET mode from Classic to Integrated.

I too had the same issue with the media page constantly loading (spinning icon in right hand panel). Including the following exceptions to my lowercase rewrite rule fixed this issue.

<conditions logicalGrouping="MatchAll" trackAllCaptures="false">
  <add input="{URL}" pattern="Umbraco/(.*)" negate="true" />
  <add input="{URL}" pattern="base/(.*)" negate="true" />

etc...

Just as a note for other people running in to this:

If you get this error after you've upgraded from an older version of Umbraco make sure that your replace the Umbraco Module in the web.config;

In < httpModules>:

<add name=" UmbracoModule" type="Umbraco.Web.UmbracoModule,umbraco" /> 
<add name="viewstateMoverModule" type="umbraco.presentation.viewstateMoverModule" /> 
<add name="umbracoBaseRequestModule" type="umbraco.presentation.umbracobase.requestModule" /> 

Replace those three with:

<add name="UmbracoModule" type="Umbraco.Web.UmbracoModule,umbraco" /> 

(note that this one has the space before "UmbracoModule" removed, something we later fixed in v6).

And in < modules> remove:

<add name=" UmbracoModule" type="Umbraco.Web.UmbracoModule,umbraco" /> 
<add name="viewstateMoverModule" type="umbraco.presentation.viewstateMoverModule" /> 
<add name="umbracoBaseRequestModule" type="umbraco.presentation.umbracobase.requestModule" /> 

Replace with:

<add name="UmbracoModule" type="Umbraco.Web.UmbracoModule,umbraco" /> 

(note that this one has the space before "UmbracoModule" removed, something we later fixed in v6).

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