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Blender 3D is in development, some problems my occour. But you can try export simple models (two cubes riged by two bones )step by step and verify the bones names, vertex groups names etc.. to discover some clue in Blender (try old Blender versions) . Some times long names are not readable by software, characters stranges my cause problems (try use only simple names like: bone1, arm2...etc)
Some times softwares not understand multiples objects in the model.
And some software don't have a pattern in the file format and unfortunately export dameged files.
These tips fits all software not only exclusive of Blender.
Good luck.
