My guess here is that there is an object in the scene named eye_l, so when it goes to export the animation, and create the morph and keys, it tries to rename the morph it creates, but fails because eye_l already exists. That’s my assumption here. Check your file to see if there is an eye_l in the scene somewhere (and if there is, try renaming it and see if that resolves the issue). Could be a mesh or a bone or whatever.