@intern_ajay welcome to the KNIME forum. I think I have seen this problem somewhere. You might want to download the example again and make sure you have the latest version of GPT4All installed and you might have to download (and select) a .gguf model again.
Also make sure you download the entire workflow group. The folder for the .gguf should be present. The selection should look something like this (depending on which models you try to use):
What operating system are you using?