The latest RhinoWIP (5E199w) has a new Preference called Files…
You can find this by navigating to RhinoWIP > Preferences > Files…
This preference tells Rhino where to look for linked textures and blocks.
This is particularly useful for office networks where there is a shared network volume where blocks and textures are stored and then referenced across multiple projects. This should also help alleviate situations where hard-coded file paths were used in Rhino 5 for Windows that did not work in Rhino 5 for Mac and vice versa.
You can also drag folders from the Finder into the File search paths list and it will add the path to that folder.
Click and drag the File search path entries up and down reorder them.
Please give this feature a try.