Trying to backward through the graph a second time, but the buffers have already been freed. Specify retain_graph=True when calling backward the first time

[neerajprad]

I think the bug might be somewhere in your model or guide, so please post the complete code. It will be much more readable and easier for others to replicate if you were to post your code inside code blocks as below:

```python
# code 
x = y