Our production File Manager page started failing two days ago with the following error:

Error: Digital Asset Management is currently unavailable. DotNetNuke.Services.Exceptions.ModuleLoadException: Sequence contains more than one matching element ---> System.InvalidOperationException: Sequence contains more than one matching element at System.Linq.Enumerable.Single[TSource](IEnumerable`1 source, Func`2 predicate) at DotNetNuke.Modules.DigitalAssets.Services.Factory.get_DigitalAssetsController() at DotNetNuke.Modules.DigitalAssets.View..ctor() at ASP.desktopmodules_digitalassets_view_ascx..ctor() at __ASP.FastObjectFactory_app_web_l5faym1v.Create_ASP_desktopmodules_digitalassets_view_ascx() at System.Web.UI.TemplateControl.LoadControl(IWebObjectFactory objectFactory, VirtualPath virtualPath, Type t, Object[] parameters) at System.Web.UI.TemplateControl.LoadControl(VirtualPath virtualPath) at DotNetNuke.UI.ControlUtilities.LoadControl[T](TemplateControl containerControl, String ControlSrc) at DotNetNuke.UI.Modules.WebFormsModuleControlFactory.CreateModuleControl(TemplateControl containerControl, ModuleInfo moduleConfiguration) at DotNetNuke.UI.Modules.ModuleControlFactory.LoadModuleControl(TemplateControl containerControl, ModuleInfo moduleConfiguration) at DotNetNuke.UI.Modules.ModuleHost.LoadModuleControl() --- End of inner exception stack trace ---

This is on a DNN PLATFORM v09.02.01 (533) build.

In a test environment reproduced the error with a fresh database and file system restore from production. Upgrading this test environment to the new v09.03.02 release did not fix the issue. (Nor did it remove Manage > File Manager and add Content > Assets to the persona bar.)

Searching this error, I see several other posts with the same error but not with a resolution. I have searched dbo.Files and dbo.Folders for any apparent duplicates, and I don't see any. I also tried deploying some code to the test environment to force a FolderManager.Instance.Synchronize(), which ran without error but also did not correct the error.

At this point our production site admins have no way to manage site content. Can anyone recommend where I need to look to resolve this error?

Apparently the underlying issue is that there is more than one digital asset controller somehow. I pulled the DNN source, compiled a debug version of the DigitalAssets module, and identified the exception at Services > Factory.cs line 49. When I changed it from:

return dac != null ? dac.Value : controllers.Single(c => c.Metadata.Edition == "CE").Value;

to:

return dac != null ? dac.Value : controllers.First(c => c.Metadata.Edition == "CE").Value;

The error went away and the module loaded correctly. Obviously I can't deploy this to production, or at least I would really prefer not to.

So question number one is: Where are the controllers actually installed at? How can I find and remove the extra unexpected digital asset controller?
Question number two is: Is this a legitimate bug, and should I submit a pull request making the change? I suspect not, but I feel like the code is making a bad assumption and it should handle it more gracefully.

No, this has only ever been a community edition, upgraded continuously since version 4. And yes, the explicit problem is that there are now two digital asset controllers. So where did the second one come from, and how do I remove it? The problem started happening spontaneously last week, but no upgrade or new modules have been installed recently.