This has driven me crazy so many times, and I always forget how to fix it, but this is what's typically awry for me: in the Organization dialogue box, under the References tab, there's a Settings button; on the lowest setting (Use this method to reference Vectorworks files) the FIRST circle (Design layer viewports) needs to be chosen. Hope this helps, if this was still a problem, or if anyone new is coming to this thread like I was today!