  We revisit the mass properties of the lensing cluster of galaxies MS2137-23
and assess the mutual agreement between cluster mass estimates based on
lensing, X-rays and stellar dynamics. We perform a thorough elliptical lens
modelling using arcs in the range 20<R<100kpc and weak lensing (100<R<1000kpc).
We confirm that the dark matter distribution is consistent with an NFW profile
with high concentration $c=11.7\pm0.6$. We further analyse the stellar
kinematics data of Sand etal(2004) with a detailed modelling of the los
velocity distribution of stars in the cD galaxy and quantify the small bias due
to non-Gaussianity of the LOSVD. After correction, the NFW lens model is still
unable to properly fit kinematical data and is twice as massive as suggested by
X-rays (Allen etal2001). The discrepancy between projected and tridimensional
mass estimates is studied by assuming prolate (triaxial) halos with the major
axis oriented toward the line-of-sight. This model well explains the high
concentration and the misalignement of 13 deg between stellar and dark matter
components. We then calculate the systematic and statistical uncertainties in
the relative normalization between cylindric M(< R) and spherical M(< r) mass
estimates for triaxial halos. These uncertainties prevent any attempt to couple
2D and 3D constraints without a complete tridimensional analysis. Such
asphericity/projection effects should be a major concern for comparisons
between lensing and X-rays/dynamics mass estimates.
