I was able to fix it in my test scenario. Here is how you can fix it on your side.
- Please make a backup of the GIFsquid.bat file found in "C:\Program Files\Adobe\Adobe After Effects CC 2015.3\Support Files\Scripts\ScriptUI Panels\GIFsquid".
- Right click the GIFsquid.bat file and select 'edit'
- Press Ctrl-A to select all the contents, then Delete to clear out the file
- Copy all the text from https://pastebin.com/raw/Ubc8bdxF into the now-empty file
- Save the new GIFsquid.bat file
- Try squirting another GIF!