I have my rocker switch on the left hand CH yoke programmed for elevator trim up/down through FSUIPC, and no problems at all.

delete it all out of FSX and then set it up in LINDA or FSuipc - and seems you need Elec Hydraulic pumps on for it to work both ways.

Here's the likely problem. The 737 has a trim lockout feature incase you have a runaway stabilizer trim. The idea is if the trim runs away in one direction you will be applying force on the yoke in the other direction. When this is sensed it will shut off the electric stabilizer trim in the direction opposite of the direction you are applying force. it is likely the simulation is sensing yoke deflection so it is locking out the trim in the other direction. The CH yoke has very low centering force not to mention that big trim wheel on the front so it can be a problem.

Hmmm a possible explanation, but if this the case, how comes when the issue occurring you can click in the trim wheel in the vc and trim both directions?

Here's the likely problem. The 737 has a trim lockout feature incase you have a runaway stabilizer trim. The idea is if the trim runs away in one direction you will be applying force on the yoke in the other direction. When this is sensed it will shut off the electric stabilizer trim in the direction opposite of the direction you are applying force. it is likely the simulation is sensing yoke deflection so it is locking out the trim in the other direction. The CH yoke has very low centering force not to mention that big trim wheel on the front so it can be a problem.

Thanks, This put me on the track and I took a look at the calibration in FSUIPC and it was showing yoke pushed forward. Can't work out why at all as it was working perfectly. I just reset the zero for it and trim is back working. Have tried re-calibrating the yoke through FSUIPC and through Windows but seems to have push forward. Oh well it can be corrected by FSUIPC and is now working again.