the one time i saw this message incorrectly in a browser was when AVG quarantined my app (and an exe in the clarion/bin folder!), scared me, but it happened only once.
not your problem i think...
in nt7 the version for this checking is at the top of netweb.js
if your clients netweb.js says 5.48, its not what you want., you need one that says 6.42
(its also in the files that combine jscripts eg: all.js and the gzipped versions, so if those get mismatchedwith you server settings you might have an issue)
or its something else...