Couple of possibilities here, TT. 1) Your gear was up (yeah, pretty obvious but I had to say it), 2) your gear was damaged in some fashion (like tail-wheel damaged), or 3) your wheels got caught in some discontinuity in the terrain. In WB, there are spots in the NG terrain, for instance that resemble a curb or step; you can't see it from inside your A/C, but its there. I've not had any trouble taxiing to and fro, even over minor hills and such. Try it off line and see what happens.
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Rojo (S-2, The Buccaneers)