Not really a viewer bug...
The grid login authentication parameters changed (without even a forewarning from LL's part: I discovered about them
by pure luck), and this broke login for most old viewers (those which did care for actually checking the login parameters, which was the Cool VL Viewer's case; some others will crash, and a few might ignore them and subsequently manage to log in nevertheless, or just don't quite crash, by pure luck).
The Cool VL Viewer v1.26.22 is deprecated, not supported, and will not be able to connect to the SL grids any more. Please use
v1.26.24.2 or newer (any older version will fail to login in SL).
Please direct any complaint for breaking old viewers login to LL, since I cannot do anything about it on my side. Note that LL
could make the login compatible again with old viewers by just returning the new parameters when the viewer requests them on login (meaning viewers that do not know about them won't request them and won't get them, getting instead the old, compatible set of parameters).