xtra error when trying to view shockwave dxr file

When trying to view a shockwave dxr file I get an error:

"This application requires an Xtra (DirectMediaXtra) that either does not exit or failed to initialize properly. Please make sure the appropriate Xtras are in the Xtras folder(s)."

This only happens with some dxr files, not all.

Any help?

thanks