My wiimote lost sync, so I attempted to resync with the red buttons. Didn't work.
I put in fresh batteries in case they were getting low, but resyncing still didn't work. Attempted resync several times after unpowering the Wii, unplugging the sensor bar, and plugging back in.
I'm using a new 4.3u Wii softmodded exactly per mauifrog's tutorial. No problems whatsoever to date.