his first post said the FRONT wheels..not the rear wheels.yup, my guess is your rear axle splines are stripped, but when in reverse there is a little more edge to grab but forward is gone
this is a known weak link on all tubed rear axle honda 4x4 atv's
the issue is , the left rear wheel has just one bearing and seal and the right side had two
the left seal lets water in as slop develops, and then that water gets in and rusts out the splines on the axle,
and BOOM, NO more rear drive(front is a limited slip, so thus one wheel only)
SO< get all 4 wheels up off the ground and see how much slop ins in your wheel bearings, adds are again, the rear left is bad(or was and damage was already done and its just took a while to rust them splines off
Good news is, a whole new rear axle is NOT that costly, and its a rather easy job with basic tools and simple repair skills!
I know this as I have a 1999 model and it happened to me
I now inspect and repair bearings way more often!, bearings are WAY cheaper than a whole new axle!