Battery problem or Optimate problem...?

[GrahamB]

I would guess it's your battery. Sounds like the optimate is doing its best to put some life in to it from very very dead which could be why you only get the green light initially. Riding the bike is giving it a bit of juice enough for a few starts but lights on with no engine is just killing it dead. Optimate "might" rescue it if you give it long enough but don't bank on it.