I've had the same problem on my WinXP system...
My TV-card is a Hauppauge WinTV PCI card with radio, teletext and remote control.
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Media Jukebox 8.0.331
Install Path: C:\Program Files\J River\Media Jukebox\
CPU: Intel Pentium II 348 MHz MMX
Memory: Total - 261 MB, Free - 99 MB
OS: Microsoft Windows XP Workstation 5.1 (Build 2600)
Internet Explorer: 6.0.2600.0000
ComCtl32.dll: 6.00.2600.0000
Shlwapi.dll: 6.00.2600.0000
Shell32.dll: 6.00.2600.0000
wnaspi32.dll: N/A
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When I still used version 8.0.293 I had no problem.
Then I upgraded to version 8.0.314.
I also tried 315 & 318; now I've got 331, but still no luck...
Deleting the registry key mentioned above did not work for me.
B.t.w., the error message window is titled "PlaybackEng". Could it help to replace the new playbackeng.dll with the older one (from version 293)? Or would this mess up things?