Rich, just to clarify my earlier post, my problem with the spacebar was that it was not sensitive enough. It really does sound to me like Half-Saint's problem is the same I had. I tried one from a brand new keyboard and still had the same symptoms.
On my machine at least, these little plastic rods were just a fraction too long. This might have been because the rubber covering the switch beneath the spacebar had lost some of its bounce with age; or it might be that the plate on which the keyboard is mounted had settled on the surface below more snugly than Psion originally intended. Either way, a little gentle sanding was the simplest solution to my situation. But building up the surface underneath the spacebar directly above the switch might also work.
just wanted to let you know I solved the problem. What I did was cut a round piece of thick paper, slightly larger than the rubber dome and insert it between the rubber dome and the keycap. It now works like new However, I think that the solution suggested by Bruni might be a more permanent one since paper degrades over time. I'll see what happens in the following weeks.
However, I think that the solution suggested by Bruni might be a more permanent one since paper degrades over time. I'll see what happens in the following weeks. 
