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When I open many projects at once and at least one of them have a reference problem, I get the following warning in a dialog window: "Reference Problems One or more project resources could not be found. Right-click the project in the Projects window and choose Resolve Reference Projects tod find the missing resources" It doesn't say what project has the issue though - I guess that dialog assumes only one project is opened at each time.
*** This issue has been marked as a duplicate of 123464 ***