Launch Voyence Control (4.0): Java WebStart failure

From the Voyence server's HTML page in IE8, I click launch Voyence Control.

Then, winindex.html says:

Java WebStart

Before installation, you must have the following installed on your computer.

You must have Java Runtime for Windows, version
1.5.0_XX. If not, click here to download and install.

So I clicked the link and installed J2SE Runtime Environment 1.5 Update 14 (published by Sun), and rebooted.

BTW, I also have Java (TM) 6 Update 22 (published by Oracle).

Something is apparently interfering with IE8 being able to find the suitable javaws, because I keep getting thrown back to the winindex.html page demanding 1.5.0_XX, even though it's already there.  (If I re-click the installation link, it eventually tells me that I already have it.)

What do I need to do?

Thanks.

Jack