I think I can reproduce, although this is not a crystal in the matter. Project + Properties, Resources and enter the name of the string resource, for example "foo.bar", which triggers this warning.
Yes, you cannot suppress this warning; it is created by the resource developer in the IDE. When it automatically generates code from the Properties \ Resources.resx file to the Properties \ Resources.Designer.cs file. Look at the .resx file and check the "name" attribute on the <data> elements. A period in the attribute value will trigger a warning.
A carefully crafted regular expression search and replace can fix this by turning periods into underscores. This gives me personally two problems, I will just write a small program that uses XDocument. Also check if you need this automatically generated code, it looks like you are replacing it.
Hans passant
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