404. That’s an error.
The requested URL /catalog/product_compare/add/product/4/uenc/aHR0cDovL2Fyb21hb25saW5lLmNvbS5ici9wZXJmdW1lcy1tYXNjdWxpbm9zLWFiYy5odG1sP2Rpcj1hc2Mmb3JkZXI9cG9zaXRpb24,/form_key/yu5AhIRqwibk6OSs/
was not found on this server. That’s all we know.