Oddly enough I CAN get up ALL the ramps when I run it in the testing grounds. In a real CW match however you walk up all the way to the top and then can't advance any further.
So the only way to get up is one of the left-side ramps with has earth/stone next to it... still, rather silly if your mech (designed for rough terrain) can't get up a RAMP
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PS: There's also a thread in the archives about this, but since it's in the archives I can't post there. One of the Admins replied that he couldn't replicate this... might be because it DOES work in testing grounds. Please look into this and fix it.