NIOS Ethernet giving "no free buffers for rx" when ISR hit

Finding documentation has been a struggle with this project.

There seems a lack of "how to" with explanation. There are examples which do not explain themselves at all. There is deep documentation that goes into details far more than a "user" of an IP block should need.

So... which documentation? I have built up sufficient "know how" from the spectrum of docs in order to get a design that works. No single document.

This was posted three weeks ago, so I have moved on somewhat. The design is working most of the time, but I am not 100% sure that this error did not appear while I was testing on Friday. The error message is fairly obtuse and diagnosing is not simple. So any advice on its meaning/cause would be useful.