MapAssist initially requires the D2:LoD folder for its libraries and data files.
maserver.exe, which constructs maps, was compiled by its authors to work with D2:LoD data, not D2R.
so… just download the installed D2:LoD folder, for example from the sources of the alternative maphack project: 1.88 GB file on MEGA
and point MapAssist to this folder