occasionally, TMPGEnc will hang when I hit Start

[chowder]

I'm using TMPGEnc 12f and h, with Avisynth plugin beta37 framserving from Premiere 6.01 in Win98SE.
What's weird is that about 60% of the time, pressing "Start" in TMPGEnc won't actually start encoding, but hang it instead. If I close the frozen program in Task Manager, and look at the Avisynth window, I can see that the audio/video frames have progressed ever-so-slightly and stopped. Most of the time, if I just fire up the frameserve process again, TMPGEnc's "Start" button will work. I'm puzzled.
Has anyone seen this behavior, and/or found a clue to its odd behavior? Right now, it's unpredictably annoying, but no big deal.
Thanks.

[chowder]

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