Copy plugins folder of K-Meleon (or Firefox or any Gecko browser) version where the plugin works properly to 1.5. Actually You need the flash supporting dll only - but why search it out?
BTW - IMHO it is bad that there is no autofind for some plugins.
p. s. The responsible plugin is the Netscape type flash plugin.
It must be installed/active to play flash.
It is in the mentioned plugins folder - You/I do not always install it new - but You need its presence. This specific plugin (additionally) sometimes has install problems. Once it has installed properly for any Gecko (or alternative non IE browser) You can use the dll which is in the plugins folder to do the actual work for any non IE browser. Sort of: Fire & forget for browsers = copy dll to the needed location & forget.
IE 6 uses the activeX version of the flash plugin. You can use it with K-Meleon also but it is harder to configure = I do not recomended to use it e.g. for safety reasons. Micosoft chose to change from Netscape plugin type to activeX at the 2nd update for IE 5.5. Before that all browsers used the same plugin type. On some systems the needed dll are repored to be still stored under IE plugins directory.
So that is the alternative location to look for Netscape plugins.
I have no idea why.