Fix: “The Global element ‘xx’ has already been declared” warnings in config files after .NET framework upgrade in Visual Studio solution

Had just converted to target .NET framework 4.7.2 a Visual Studio solution full of 4.5 libraries, console apps and an MVC 5.0 (recently converted from 4.0) web app and all seemed to build fine, but then noticed that with web.config of the MVC web app open in the editor, it was showing lots of warnings of the form:

The Global element ‘xx‘ has already been declared in …

and marking them in the text with blue underscores under some whitespace

Seems others have had this issue too with configuration files (both ASP.net and Entity Framework ones) after changing target .NET framework:

https://stackoverflow.com/questions/11816916/fix-the-global-element-configuration-has-already-been-declared

Luckily the solution was hidden in that thread, just had to pick the best one (read on below)

– at https://stackoverflow.com/a/52274659/903783 one reads (see related screenshot there):

I noticed this issue with my VS2017.

Changing DotNetConfig.xsd to use "Automatic" solved the problem.

This doesn’t seem to work permanently (only worked once for a while for me)

– at https://stackoverflow.com/a/28114738/903783 is says:

With the symptoms as described in the question, and using Visual Studio 2013 (Update 4), I could see in the XML Schemas [sic] dialog that both DotNetConfig.xsd and DotNetConfig40.xsd were selected for use.

I’m using a .NET Framework 4.0 project.

The two XSD files conflict with each other, each defining the same elements, causing the warnings to be emitted.

These schema files are contained in the %programfiles(x86)%\Microsoft Visual Studio 12.0\xml\Schemas\ folder.

DotNetConfig.xsd is in the 1033 sub-folder and appears to be the newer, more complete version.

No matter what settings I selected in XML Schemas, I could not deselect, or remove DotNetConfig40 nor DotNetConfig. I tried "Remove", and changing the Use parameter from "Use this schema" to "Automatic" and then "Do not use this schema".

No matter what was selected, for either file, when I would return to the dialog, both would be selected for use. I also tried the trick of moving to another row before pressing "OK" to no avail.

Finally, I renamed the DotNetConfig40.xsd file to DotNetConfig40 DO NOT USE.xsd to prevent it from being loaded. This immediately solved the problem.

This does work (adapting the path for VS2017), but one isn’t sure (unless they check the file dates maybe) which file to keep, in my case it was 1033/DotNetConfig.xsd and DotNetConfig45.xsd, nor are they sure this won’t cause any side-effects in other solutions/projects.

– Finally, at https://stackoverflow.com/a/33823331/903783 it read:

I struggled with this for a while as well. Turns out, my version of the problem originated from the hidden {PROJECTNAME}.SUO file created by Visual Studio.

My guess is, VS will cache the XSD schema associations in this file. The warnings popped up after I changed the target framework, and they disappeared after I deleted the SUO file and restarted VS.

This fixed it permanently. Deletion of the .suo ended up with the DotNetConfig.xsd and removed the DotNetConfig45.xsd from the XML schemas list for the projects in the solution. In fact I deleted just a .suo file with no filename part, just a file extension, found by typing “.suo” at the search filter in the top-right of the solution’s folder window in Windows 10 File Explorer.