I would recommend medical booze, as we call it here in Sweden. It is 96% alcohol which can be bought in a pharmacy. It wount affect any kind of hard plastics I think. My suggesting is to drip it on cotton pins, what we call Topz. Then clean all contacts.
Found this on a photo community:
"Usually error 99 means that your lens contacts (maybe in the body, or the lens itself) is dirty.
I got this from the web and saved it in my laptop just in case I get the same error:
1. Carefully clean the 8 gold color lens contact pins on the camera body
lens mount with a pencil eraser. Do this while holding the camera so that
any eraser dust will not fall into the camera.
2. Take out both batteries. Yes, there are 2. I had forgotten about the
smaller Date/Time battery. Also remove the CF memory card.
3. With the batteries removed, turn the camera switch on for 3-5 minutes.
He said that this clears the memory.
4. Turn the camera off and put the batteries and CF card back in.
5. Re-attach the lens and turn it back on. "