I had the same problem.
I have an old video card, a GeForce 8800 GS.
I changed the setting under "Main tab --> Express Setting --> Driver" from Waifu2X NCNN Vulkan to Waifu2X Caffe,
and under "Driver Settings --> Process" from gpu to cpu, and the problem was solved.
You can try changing the same parameters as I did, or experiment with other available options in those sections.
I had the same problem. I have an old video card, a GeForce 8800 GS. I changed the setting under "Main tab --> Express Setting --> Driver" from Waifu2X NCNN Vulkan to Waifu2X Caffe, and under "Driver Settings --> Process" from gpu to cpu, and the problem was solved.
You can try changing the same parameters as I did, or experiment with other available options in those sections.