Based on the error message self.OpenAsArray(idx, invert=True) seems to be a TiffImageFile, which cannot be transformed to a PyTorch tensor and thus this line of code raises the error:
x = torch.tensor(self.OpenAsArray(idx, invert=True), dtype=torch.float32)

You would thus have to make sure to transform this TiffImageFile to e.g. a numpy array before and transform it to a tensor via x = torch.from_numpy(np_arr).