This would indicate that the VRML file is invalid, unuspported format, or different version. Because Cortona is able to read the file, probably it's valid but a different format or version. Please inspect the VRML file in a plain text editor (e.g. the MATLAB Editor). It should start like this:
#VRML V2.0 utf8
If it doesn't, the file is not VRLM97 and cannot be used without being converted to VRML97 first. Several tools, like e.g. the included V-Realm editor, can be used to do the conversion.
