It looks like you're using the /{Assembly};{path/to/Image}
construct without the pack://
uri prefix. The editor is warning you that it can't find the file because it doesn't really understand the Uri (until the application is actually built). It'll be defaulting to looking on the file system and trying to prefix it with file://
, which of course results in a relative uri to the working directory of the Visual Studio process.
I suspect that if you explicitly include the pack://
uri prefix, that the editor will stop complaining.
pack://application:,,,/Midas;component/Images/Actions/Delete.ico
That way the designer will just know that it should not be trying to look for a file://
location.