Fatal Error when opening View Level?

[Citation_Needed]

If, heaven forbid, someone still checks this area of the forums, perhaps you could help me figure out a little problem I have?

I have been trying to get into mapping for xenonauts, however, It seems I can`t even use the editor, whenever I try to open the Level Viewer, I get this, does anyone know what is causing this or how I can fix it?

Thanks.