Thanks, that worked - although I had to jump through some unexpected hoops. Flipping it and resaving it did no good, so I tried the problem texture on the arm I knew was working... same issue, which meant I at least knew it was definately the texture.

Ended up cutting the texture from the working side, pasting it into a enw document in photoshop then saving it under a brand enw name and importing it manually... then it worke fine.

Weird, but sorted - thanks :)