The input to the network is expected to be in a BCHW form, i.e. a 4-dimensional Tensor, where the first dimension is the batch dimension, the second dimension is the number of image channels (3 for color, 1 for grayscale), the third dimension is the image height, and the fourth dimension is the image width.
Your input is 2048x1x1 according to your error message. So pytorch thinks the last two dimensions are height and width, i.e. that you have a 1 pixel image. And if you try to do 2x2 pooling on a single pixel, you get the error you see (you need at least 4 pixels in a 2x2 grid).
I suspect you have an error in the way you transform images into your input tensor. Are you using torchvision.datasets?
Stephen