What's funny is this is the second post with that exact same switch broken on a HS this month...

http://pinside.com/pinball/forum/topic/very-weird-hs-problem

and another post about the switch just to the left of 43... #42.

http://pinside.com/pinball/forum/topic/how-to-adjust-switch-42-on-high-speed-pin-ball

Try starting in those two postings; or if all else fails start at RTFM...

http://mirror2.ipdb.org/files/1176/Williams_1986_High_Speed_Instruction_Manual.pdf

It would at least tell you what switch 43 is. (hint: so do the other two posts)

How to Adjust: (To quote the other posting: Carefully!)
What does it do: Senses a ball passing over it.

P.S. Adjusting means fix, (maybe wiring, maybe switch, maybe screws, etc.) It rarely means bend the crap out of....

P.S.S. If you're going to do more than a flyby and really want help, then explain a little more what the problem is, we'll be happy to help, but your first post seems to be short and demanding.

Remember that the game does not know what's wrong with the switch, just that it hasn't registered in quite a while. There might not actually be anything wrong with it if it has not been activated in a game for a long time.
Try manually activating the switch while running a game before anything else.
If that doesn't clear the error, test the switch in test mode before you "fix" anything.

I have had switch errors show up that were just "Hey, no one has hit this switch in a long time" on more than one pin.