This took me some time to debug, as the form-element only reports "value is invalid" and no exceptions were in the profiler, but in NumberToLocalizedStringTransformer line 130+

    if ($result >= INF || $result <= -INF) {
        throw new TransformationFailedException('I don\'t have a clear idea what infinity looks like');
    }

values are reverseTransform'ed and tested against INF. On Solaris however, for years INF equals float(0), so the above test always returns true making it impossible to use the Form framework on Solaris hosts.