toushirou1989 - Thanks for posting your question on the forum!
It appears the first entry on your table above is what is supposed to be your default route, but the subnet mask is incorrect. Instead of '255.255.255.255', the mask should read '0.0.0.0'. Once this change is made it should be recognized as the default route.
If this does not resolve the issue, can you please respond with the firmware you are running, and what page you are seeing that error on?
Please do not hesitate to let us know if you have any questions.