  It is generally accepted that experiments at an e+e- linear colliders will be
able to extract the masses of the selectron as well as the associated
sneutrinos with a precision of ~ 1% by determining the kinematic end points of
the energy spectrum of daughter electrons produced in their two body decays to
a lighter neutralino or chargino. Recently, it has been suggested that by
studying the energy dependence of the cross section near the production
threshold, this precision can be improved by an order of magnitude, assuming an
integrated luminosity of 100 fb^-1. It is further suggested that these
threshold scans also allow the masses of even the heavier second and third
generation sleptons and sneutrinos to be determined to better than 0.5%. We
re-examine the prospects for determining sneutrino masses. We find that the
cross sections for the second and third generation sneutrinos are too small for
a threshold scan to be useful. An additional complication arises because the
cross section for sneutrino pair to decay into any visible final state(s)
necessarily depends on an unknown branching fraction, so that the overall
normalization in unknown. This reduces the precision with which the sneutrino
mass can be extracted. We propose a different strategy to optimize the
extraction of m(\tilde{\nu}_\mu) and m(\tilde{\nu}_\tau) via the energy
dependence of the cross section. We find that even with an integrated
luminosity of 500 fb^-1, these can be determined with a precision no better
than several percent at the 90% CL. We also examine the measurement of
m(\tilde{\nu}_e) and show that it can be extracted with a precision of about
0.5% (0.2%) with an integrated luminosity of 120 fb^-1 (500 fb^-1).
