  We report a strong difference in the sliding properties of the bidirectional
charge density wave (CDW) in the two-dimensional rare earth tritelluride
ErTe$_3$ which occurs below $T_{CDW1}=265$ K with a wave vector along $c$-axis
and below $T_{CDW2}=165$ K with a wave vector along $a$-axis; the excess
current carried by the motion of the CDW is 10 times less for the lower CDW
compared with the value of the upper one. We tentatively explain this result by
a stronger pinning of the lower temperature CDW intricated with the upper one,
which inhibits its motion and may generate a phase slippage lattice.
