My guess is that your saved file path_pretrained_model doesn’t contain nn.Parameters. nn.Parameter is a subclass of torch.autograd.Variable that marks it as an optimizable parameter (i.e. it’s returned by model.parameters().
If your path_pretrained_model contains Tensors, change your code to something like:
self.W_conv1 = nn.Parameter(params.items()[0])

If your path_pretrained_model contains torch.autograd.Variables, change your code to something like:
self.W_conv1 = nn.Parameter(params.items()[0].data)