you are trying to load a state_dict() of a model that trained on a single gpu to a multi-gpu with nn.DataParallel() i see.
Every model that is trained with nn.DataParallel() a .module is added to it so the weights also contains .module
for example if you have fc layer in your model, a model that is trained with nn.DataParallel you will be able to access it using model.module.fc and a model that is not trained with nn.DataParallel you will be able to access it using model.fc
simply load to weights of the model before wrapping it with nn.DataParallel