I was just logged in as Admin, and changed the setting to select the which Control Panel I want to use using the pick list provided.  I first switched to Basic, and everything was working okay.  I didn't like the Basic panel, so I went back to the appropriate setting and selected something different from the pick list (I don't remember what the option was labeled).  After I submitted the change, I got this error:

An error has occurred.
DotNetNuke.Services.Exceptions.PageLoadException: Could not load type 'DNNC.Control.Panel'. ---> System.Web.HttpParseException: Could not load type 'DNNC.Control.Panel'. ---> System.Web.HttpParseException: Could not load type 'DNNC.Control.Panel'. ---> System.Web.HttpException: Could not load type 'DNNC.Control.Panel'. at System.Web.UI.TemplateParser.GetType(String typeName, Boolean ignoreCase, Boolean throwOnError) at.....

etc.

Now I can't log in as an admin at all.  As soon as I'm authenticated, I get this same error and I'm unable to see any menus so that I can change this setting back.

Is there an editable config file somewhere that I can change the setting back to my old control panel?  If so, where can I find it and how do I alter it to get back the Basic Control Panel?  

Or, is there another way I can resolve this issue without compromising the integrity of my website?

Thanks - your help is very much appreciated.

Thanks Sebastian.

I believe we're running version 4.9 (I'm unable to log in to double check).

Once I've located the path to the control panel, are you able to tell me the new value I should be using to replace it?

in SSMS; go to table dnn_hostSettings. Select "edit top 200 rows from context menu and in line with settingname  "ControlPanel" enter "Admin/ControlPanel/IconBar.ascx". as soon as you left the line, it gets persisted. restart your app pool and the control panel should show up.