Sure. It seems that the problem come from the very first sample:
code I execute:
for data, target in federated_train_loader:
        print(data.shape)
        print(target)
        print(1)
        output = model(data)
        print(2)

Error I have:
torch.Size([64, 3, 224, 224])
(Wrapper)>[PointerTensor | me:36484845200 -> bob:18563538231]
1
---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
<ipython-input-25-09bbd3d5a518> in <module>
      3         print(target)
      4         print(1)
----> 5         output = model(data)
      6         print(2)
      7 

~/miniconda3/envs/pysyft/lib/python3.7/site-packages/torch/nn/modules/module.py in __call__(self, *input, **kwargs)
    491             result = self._slow_forward(*input, **kwargs)
    492         else:
--> 493             result = self.forward(*input, **kwargs)
    494         for hook in self._forward_hooks.values():
    495             hook_result = hook(self, input, result)

~/miniconda3/envs/pysyft/lib/python3.7/site-packages/torchvision/models/vgg.py in forward(self, x)
     42         x = self.features(x)
     43         x = self.avgpool(x)
---> 44         x = x.view(x.size(0), -1)
     45         x = self.classifier(x)
     46         return x

~/miniconda3/envs/pysyft/lib/python3.7/site-packages/syft/frameworks/torch/hook/hook.py in overloaded_native_method(self, *args, **kwargs)
    675                 # Send the new command to the appropriate class and get the response
    676                 method = getattr(new_self, method_name)
--> 677                 response = method(*new_args, **new_kwargs)
    678 
    679                 # For inplace methods, just directly return self

~/miniconda3/envs/pysyft/lib/python3.7/site-packages/syft/frameworks/torch/hook/hook.py in overloaded_pointer_method(self, *args, **kwargs)
    511             command = (attr, self, args, kwargs)
    512 
--> 513             response = owner.send_command(location, command)
    514 
    515             return response

~/miniconda3/envs/pysyft/lib/python3.7/site-packages/syft/workers/base.py in send_command(self, recipient, message, return_ids)
    425 
    426         try:
--> 427             ret_val = self.send_msg(codes.MSGTYPE.CMD, message, location=recipient)
    428         except ResponseSignatureError as e:
    429             ret_val = None

~/miniconda3/envs/pysyft/lib/python3.7/site-packages/syft/workers/base.py in send_msg(self, msg_type, message, location)
    221 
    222         # Step 2: send the message and wait for a response
--> 223         bin_response = self._send_msg(bin_message, location)
    224 
    225         # Step 3: deserialize the response

~/miniconda3/envs/pysyft/lib/python3.7/site-packages/syft/workers/virtual.py in _send_msg(self, message, location)
      8 class VirtualWorker(BaseWorker, FederatedClient):
      9     def _send_msg(self, message: bin, location: BaseWorker) -> bin:
---> 10         return location._recv_msg(message)
     11 
     12     def _recv_msg(self, message: bin) -> bin:

~/miniconda3/envs/pysyft/lib/python3.7/site-packages/syft/workers/virtual.py in _recv_msg(self, message)
     11 
     12     def _recv_msg(self, message: bin) -> bin:
---> 13         return self.recv_msg(message)
     14 
     15     @staticmethod

~/miniconda3/envs/pysyft/lib/python3.7/site-packages/syft/workers/base.py in recv_msg(self, bin_message)
    252             print(f"worker {self} received {sy.codes.code2MSGTYPE[msg_type]} {contents}")
    253         # Step 1: route message to appropriate function
--> 254         response = self._message_router[msg_type](contents)
    255 
    256         # Step 2: Serialize the message to simple python objects

~/miniconda3/envs/pysyft/lib/python3.7/site-packages/syft/workers/base.py in execute_command(self, message)
    363             else:
    364                 try:
--> 365                     response = getattr(_self, command_name)(*args, **kwargs)
    366                 except TypeError:
    367                     # TODO Andrew thinks this is gross, please fix. Instead need to properly deserialize strings

~/miniconda3/envs/pysyft/lib/python3.7/site-packages/syft/frameworks/torch/hook/hook.py in overloaded_native_method(self, *args, **kwargs)
    661                 except BaseException as e:
    662                     # we can make some errors more descriptive with this method
--> 663                     raise route_method_exception(e, self, args, kwargs)
    664 
    665             else:  # means that there is a wrapper to remove

~/miniconda3/envs/pysyft/lib/python3.7/site-packages/syft/frameworks/torch/hook/hook.py in overloaded_native_method(self, *args, **kwargs)
    655                 try:
    656                     if isinstance(args, tuple):
--> 657                         response = method(*args, **kwargs)
    658                     else:
    659                         response = method(args, **kwargs)

RuntimeError: shape '[0, -1]' is invalid for input of size 1605632