The configuration element is not declared
Go to XML menu (visual studio top menu item) choose schemas and find for DotNetConfig.xsd and choose Use this schema.
Your problem will resolve for sure
<configuration xmlns="schema URL"> <!-- configuration settings --></configuration>do changes,like above & try
I had the same issue. It is not an error, it is simply a warning; so your application should still compile. I used the following simple config file and the warning is still produced.
<?xml version="1.0" encoding="utf-8" ?><configuration> <startup> <supportedRuntime version="v4.0"sku=".NETFramework, Version=v4.5"/> </startup></configuration>It is an issue that has been raised on the MSDN website, but it does not seem to have been satisfactorily resolved. See link below: