[HELP] QTGMC Now Crashing Hybrid - Header too large?

[Mondo-A-Go-Go]

Hello, I've been using Hybrid successfully for years now to deinterlace with QTGMC (and convert colorspace from 601 to 709).
One day, it started crashing every time I attempted to deinterlace (with whatever version I had been using successfully for a long time). I updated to the latest Hybrid version and am having the same issues.

My Hybrid version is 2026.03.21.1 on Windows 10 64-bit.

My typical workflow is:

• Input an Uncompressed AVI, ProRes 422 HQ, or FFV1 Matroska
  
• Processing-- Video: ProRes / Audio: passthrough all
  
• Encoder: Standard / Profile: 422 HQ
  
• Deinterlace-- QTGMC Vapoursynth / Preset: Medium / Bob: Yes
  
• Vapoursynth-- ColorMatrix: From 601 to 709
  

^and that's it! This also happens whether or not I engage the colorspace conversion.

I keep getting the errors:
FFmpeg output: [in#0 @ 000001f68a421a80] Header too large.
[in#0 @ 000001f68a420480] Error opening input: Invalid argument
Error opening input file -.
Error opening input files: Invalid argument

...and then:
process finished with exitcode: -22 and exitStatus: 0

Attached is the Debug output. Unfortunately, I'm not super tech-savvy when it comes to this stuff, mainly just doing basic conversions in ffmpeg and then of course this wonderful GUI I can't wait to use again. 

[Selur]

If you updated an older version, deinstall that first and make sure the Hybrid folder is gone before installing the version.
Especially when Vapoursynth versions changed, you will need to deinstall the old version.
If that does not fix the issue, try whether the latest dev version already fixes the problem. (deinstall previous Hybrid version)
In case it does not, create a debug output when opening the Vapoursynth Preview since that should show more details.

Cu Selur

[Mondo-A-Go-Go]

Selur, you are a genius. I've finally gotten to the root of the issue, and it was due to my Norton Internet Security misidentifying a Vapoursynth .dll as a trojan horse!

Currently running your latest dev version. I did the Vapoursynth preview and it revealed that "fmtconv.dll" was MISSING. At the same time, Norton gave a pop-up that it had blocked a threat. Looking deeper I found that it removed the .dll and put it in quarantine as a trojan horse. I was able to restore the file, set a rule that it won't check it again, and boom-- Hybrid is back and running to it's old self.

Thank you so much for your help!!!! Shot an entire documentary on VHS, and now I can get back to the edit. 

(Not sure if it was the dev version, the Vapoursynth preview, or some magical combination, but I have never gotten the Norton popup before telling me that they threw away a critical piece of the software. Would never have figured this out otherwise!)

[Selur]

Happy, you found the problem and got it resolved.

Cu Selur