The problem is not with the mapeditor (as rme definitely supports 8.6) but rather with the .dat or .spr, or the configuration of the mapeditor.
Please make certain your .dat and .spr are the exact ones needed without even a byte of alteration. To make sure you can visit remeres website and download the correct tibia client, and use that .dat and .spr. If you are still having problems then it must be with the map not actually being 8.6 but rather 8.54 or something stupid like that, please try the first solution, if the problem persists, open rme by itself (without a map) and change the configurations.