Check the alignment of your wheel sensor against the pickup. If they're not lined up well you may get intermittent readings. Also try cleaning the contacts on the computer body and the mount with a pencil eraser. If the fit is loose, you could try adding a shim (maybe some folded paper) to hold the computer more tightly in the mount. Worst case is that you might have a wire coming loose either from the pickup or the mount. If that's the case then you either need to break out your soldering iron (you do have one, right?), or get in touch with Cateye.