There was some problem in the csproj file due to merging. Some files have been added twice. This caused a problem. After removing duplicates, the problem is resolved.
MSBuild and Visual Studio (at least 2015) also give this error if the EmbeddedResource element does not have its closing tag. Between the false text of the error message about the Include attribute and the absence of a line number, this may take longer than it should be monitored.