Few things you can do.
Go to Advanced Tab, there should be a section that is for fan speeds, monitoring of the fans and profiles labeled as Silent, Medium, High. Scrolling further down you will see a low RPM monitor. This is the signal when trying to post, if your fan RPM is lower than the selected RPM, it will give you the error. Change this to 600 RPM or maybe 500 RPM if you can. This will be the lowest settings, meaning unless something is going wrong with your AIO, you will bypass the screen since your RPM is already at 1100.
Second option is to plug in one of the radiator fans into the CPU_FAN header. Cable management might suffer slightly, but most of the time this is the fastest fix without tinkering in BIOS.
Third option, just disable the fan error monitoring. This is what I did on my ASUS V Rampage because the above 2 options didn't work for whatever reason; then again, that motherboard was gimmicky anyways. Disabling the fan error monitoring will never alert you if say your AIO isn't working, but at that point, that's something you should be able to notice on your own. It's more so that you don't power on a system, play, put stress on a CPU when nothing is cooling it, but again, this is something that you should notice if anything were to go wrong with your AIO. I believe to find this option is Monitor > Fan Speed Monitor and change the option to ignore.