Every time i try to export something as a jms, and error occurs and 3ds closes.

It is annoying. I'm trying to make stuff, but can't get it ingame. If someone could help, it'd be nice.

Use bluestreak, if you aren't already.

pre-export checklist:

multimaterial is assigned to the mesh(es)
bitmap assigned to diffuse of materials in multimaterial, if sub mateial is for a shader (not sky, portal, etc.)

mesh is linked to a "frame"

mesh has no open edges or isolated vertices (select the mesh, unhide all verts, select all, and click the Remove Isolated Vertices button. If the nuber of selected verts decreases, you had isolated verts)

STL Check. If it finds errors,
-Multiple edges are when more than 2 faces share an edge.
-Double faces? Uncheck Change Material ID and convert to mesh. The double faces will be selected. Select invert and hide. At each set of duplicates, hide one which faces the correct direction, and one by one delete it's duplicates. Repeat for each set of duplicates.
-Spikes, I forget how those go
-Open edges can be fixed by welding or collapsing verts or creating faces to patch the hole

That's all I can think of for now

Wait...

Multimaterial assigned to meshes?

Could it be textures that are screwing my jms up?

solved over xFire - blitzkrieg on max8. Solution: Bluestreak