Getting this problem on 3 PCs with a fresh installation of VS 2015 RTM. There are no issues when the file is opened in VS 2013. Steps described in Fix: The Global element 'configuration' has already been declared and other related questions don't help as VS ignores any changes on the XML schema dialog. Ideas?
Xml – VS 2015 RTM web.config The Global element ‘configuration’ has already been declared
visual-studio-2015web.configxml
Best Answer
Unfortunately, there are a number of situations that can cause this problem.
The most likely problem though is that the schema for the document has been set incorrectly. This can happen when you install a newer version of .NET and/or Visual Studio on the computer. The fix is simple though.
From the Visual Studio documentation:
Specifically, you want to set the "Use" column for the "DotNetConfig.xsd" schema to "Auto".