Hi!
Can you, please, post the error message here?
There are many other commands can be used before set_mw_lib_ref command, so what actually do you mean?
As I remember, mw_lib_name is the library which contains mw_cells related with other designs instantiated in your top level design (like memory, ip-blocks etc), as well as wm_cells for all your stdcell .db libraries used in your design. They contain FRAM and CELL views of your blocks and stdcells.
You can create mw_lib from .gds and .lef files using Synopsys Milkyway tool.
Guys, please, correct me if I wrong.
So, <library name> should be the same as names of your folders with mw_libs (contains CELL and FRAM folders). In can be just folder names (if you set search_path variable before with "path/to/your/mw_lib/folder/") or full path to the mw_lib folders.