My previous post has become corrupted so trying again here:

When we upgraded out 4.9.4 install to 5.1.1 the upgrade went fine, but the host file manager won't load.  The admin file manager works just fine.  Everything else that I've tested works fine. Here's the error on the host file manager page:

Error: File Manager is currently unavailable. DotNetNuke.Services.Exceptions.ModuleLoadException: Object reference not set to an instance of an object. ---> System.NullReferenceException: Object reference not set to an instance of an object. at DotNetNuke.Modules.Admin.FileManager.FileManager.get_HasPermission(String permissionKey) at DotNetNuke.Modules.Admin.FileManager.FileManager.ManageSecurity() at DotNetNuke.Modules.Admin.FileManager.FileManager.Page_Load(Object sender, EventArgs e) --- End of inner exception stack trace ---

I tried the upgrade again from a fresh backup.  Same results.  How should I proceed from here?  This is on a production machine and I'm the only host account and I have full control over the server, so do I have to have the host file manager?  But if this might come back to haunt us later I'd like to revert quickly so content workers can get back to their thing.

The only related stuff I've been able find doesn't seem helpful:

http://support.dotnetnuke.com/issue/ViewIssue.aspx?id=9877&PROJID=2

http://support.dotnetnuke.com/issue/ViewIssue.aspx?id=10119&PROJID=2

Thanks you.

Should it then be OK for me to continue with the 5.1.1 portal if I can live without the host file manager for a while?  In other words, it should be resolved by a future upgrade that won't be dependent on the prior upgrade history? Or must I revert to the 4.9.4 backup? 

Not sure DNN-10536 is the issue? This exception only occurs when you try to delete a file in Host/File Manager (see issue title).

What happens if you select Host Settings, click Add (Page) on the control Panel, select  Host as the parent page, click update (which will add a new page) and add a new file manager module?