revBrowserCallScript() not working in Mac OS X

[Slava Paperno]

My application (LC 4.6.3) does this:

revBrowserSet(sBrowserID, "htmltext", tMyHTML)

tMyHTML is a fully-formed Web page that includes this function:
function SetFontSize(FSizeStr) {
  document.body.style.fontSize = FSizeStr;
}

A button on the same card as the revBrowser instance does this:

revBrowserCallScript(sBrowserID, "SetFontSize", 16 & "px")

This works fine in Windows, but now that I started testing in Mac OS X
(10.5.8. on PPC and 10.6.8 on Intel), the line above returns "execution
error at line n/a (External handler: exception) near *** [WebUndefined
cStringUsingEncoding:]: unrecognized selector sent to instance ...."

This is my second major revBrowser surprise since I started testing in Mac
OS X. Am I on the wrong track? Does revBrowser work the same in Windows and
Mac OS X? I realize the underlying browser comes from the OS. Do I need to
do anything differently for revBrowser in Mac OS?

Thanks,

Slava