RealProducer 6.1: possible conflict on Macs with G3 upgrades

Winsor White writes about a problem he was having with RealProducer Plus G2 6.1 (see also previous MacFixIt item):

"For the first time, this release is designed to allow Mac users to record RealVideo files in real time, live, without having to record an intermediate QuickTime file first, and then encoding that file. It is a major time saver. This is a feature that has been available to PC users for quite some time. Unfortunately, it now appears that it will not work with at least some G3 upgraded Macs. Using my PPC 8500 with PowerLogix G3 300/300/1Meg G3 upgrade, I have been unable to do live encoding. I have been getting the following message error message: 'Could Not Create a Destination File.' After several exchanges with the support people at RealNetworks about the problem, it now appears that the live video encoding feature may not work with 604 machines that have been upgraded with a G3 card. (Encoding live audio and static video files works fine)."

Supporting this, Winsor sent us the following reply he received from Real Networks:

In our testing lab, we tried live encoding on a vanilla Power Macintosh 8500 with video in, and on an 8500 with video in upgraded with a 300 MHz G3 card. We could reproduce the problem you are reporting on the machine with the G3 upgrade, but not on the stock 8500.

It appears to be a problem with the encoding engine not receiving the data quickly enough on the upgraded machine, and giving up on encoding. We're investigating further, but at this point I do not have a workaround to suggest aside from removing the upgrade board or else using a different Mac for encoding.

However a further note adds that the problem may be easy to fix:

While we were able to reproduce the problem on one of those machines, it's not completely reproducible; a clean reinstall of the Producer on that Macintosh did not exhibit any problems.