At least one configuration was not loaded because it does not have a configuration name attribute
Each <Config> section in a .csproj or .vbproj file must have a Name attribute that defines a unique name for that configuration. This diagnostic indicates that the Name attribute is missing. If the Name attribute on a Configuration is missing, then that configuration will not be loaded into the project.
This error is most likely caused by editing the project file by hand.
To correct this error
Insert a a configuration name right after the <Config> line in the project file.
Name = "someconfigname"
A typical configuration name is Debug or Release.