On my last homebrew when I transferred my beer to a bucket for bottling I noticed that the top had an oily shimmer to it. When I tried the beer a few weeks later the beer came out with pretty weak head and not enough bubbly. How do I remove that oily shimmer before bottling next time? Did it cause my problems, or was that something else.
FWIW, its highly possible that the oily surface you observed is not at all related to your head and carbonation problems.
I've seen that oily 'shimmer' on the top of several beers in primary, and like you, I was worried that some soap or something had gotten in there. However, I never noticed a correlation between the oily/rainbow sheen and any head problems.
I don't know what causes that little oil slick on top of the primary, but it could just be oils from the hops or something. Perhaps an adjunct like oats can add it too, who knows? Anyway, I would just make sure next time that you rinse all your gear real well to make sure there's no cleanser left behind, but don't freak out about it too much.