You tried to Xref a file into a drawing, and you received an INVALID message in the Command line.
This issue is ususally the result of corruption in the file you're trying to Xref into your drawing.
Follow our steps to clean your Xrefs before attaching them to your drawings. Cleaning your files will rid them of corruption and should allow them to Xref properly.
Find out more about drawing corruption and learn how to avoid it. Follow our steps to prevent drawing corruption on all your drawing files and Xrefs.