The most probable reason for the problem is that you have lots of Cosmos materials in your file, and you moved to another machine, or the texture cache is cleared.
The green bar at the bottom that @Japhy is probably reading as V-Ray searching for asset, is actually Rhino searching for the textures for the viewport preview of the cosmos materials.
It can be because of two reasons:
- Cosmos assets are not available on the local machine, but Rhino doesn’t know that (yet) and it is doing its best to find the textures to display them. If you have a lot of network-ed files, that could take a while and will happen every time, unless you have the files locally
- Cosmos materials use .tx files which Rhino does not support, and we need to sample them with V-Ray to a .jpg file that Rhino understands. Depending on the texture sampling settings, this may take a while, but happens only once, as the texture cache is local to the current machine. You can significantly speed up any future samplings if you lower the sampling resolution via vrayTexturePreviewSettings command.
The error you see when rendering is probably due to the fact that you started the render process before the viewport is created (e.g. while it was still black). If that was the case try to render another viewport.