Thank you for the detailed report! From what you've shown me, I believe the issue lies with ImageMagick (convert.exe) it looks like it is unable to open the intermediary AVI file. Can you check that convert.exe isn't being blocked by Antivirus? It is in the gifsquid/bin folder
Thank you for your swift response!
Added whole GIFSquid folder (inside ScriptUI Panels) to exception, convert.exe to trusted files + set to Administrator but still no luck.
Closing completely Firewall and Antivirus made no difference.
UPDATE (Problem Solved!)
It seems there was a problem with both Avast antivirus and Comodo Firewall you can add the whole folder to be trusted and it doesn't work.
I tested few free alternatives that work and can recommend:
Firewalls: TinyWall or Simplewall
Antivirus: Bitdefender Antivirus Free or Kaspersky Cloud Antivirus
Solution: Add convert.exe to exception and something that was not mentioned here,
do the same with cmd.exe ( ! ) (you can set it for an hour or time span needed to convert file if you don't want to allow connections permanently)
It's all good now,
Thank You :)