It's just a small popup box error titled ALERT that reads "Error: Could not load game at path '.'. Is the .pck file missing?"
As for my system:
Processor: AMD Ryzen 7 5700U
Graphics: AMD Ryzen 5 Pro 4650G with Radeon Graphics
Memory: 12 GB RAM
OS: Windows 10 Home (64bit)
I'd give you a print out on my system and a screen capture of the error.... except that I don't know how to message you on itch.
I remember this game working with no issues with my prior laptop that died around September of last year. This computer had an Intel processor that was slower, 8GB ram and Intel UHD 620 graphics.
I'm just now getting around to playing Kaiju Klimb again. It's a delightful little game, so I'm very glad I was able to get past the error.