It worked!  Thanks!!
For people looking at this in the future, this is the code I used:
model.x_grid = model.x_grid.contiguous()
model.y_grid = model.y_grid.contiguous()
model.decoder.x_grid = model.decoder.x_grid.contiguous()
model.decoder.y_grid = model.decoder.y_grid.contiguous()

model.load_state_dict(pretrained_dict)

I guess since the grid tensors were not the same size in memory as the pretrained tensors the model was trying to load, even though the tensors are the same size nominally, resulting in a cryptic error message.