Ahhh, I think that
IS the solution
It seems that you have one of the first 4.00 aquaeros. The firmware 3.99d is only a changeover-firmware because the final and completly new firmware wasn't finished when AC was delivering the 4.00 aquaeros. That also means your aqauero has the old operating system which is not compatible to the aquasuite!
At first you have to update the operating system of your aquaero to version 2.03.
Download this ZIP archive and extract it somewhere.
To be sure that the update will success you should do the following.
1.) Shut down your PC and disconnect everything from your aquaero (sensors, fans, ATX stand-by, etc.). Only the power and usb connection should be attached.
2.) Back in Windows: close all unnecessary tools like virus-scanner, messenger etc.
3.) Start the 'aquaero os loader.exe' from the ZIP archive.
4.) In the menu click on Sprache and select english.
5.) Make sure that the status in the lower left corner says that a connection to the aquaero is established (if not you have to stop here).
6.) Click on the button 'flash firmware'. Confirm the warning message. Arter that you have to press and hold the set button of your aquaero for around 2-3 seconds. The update process will start now.
7.) When the update is finished you have to shutdown Windows and disconnect your PC from the power outlet for 30 seconds.
An other way would be that you only disconnect the power-cable from the aquaero and wait 30 seconds before you plug it in again.
8.) Start your PC and the display of your aquaero should say 'load news OS' and after a few seconds it sould say something like 'new OS loaded, please restart'. Shut down you PC again and repeat step 7. (disconnecting the power)!
8.) Start your PC. Windows should recognize a new device. Wait until this process has finished, repeat step 2. and then start the
latest version of the aquasuite.
9.) In the menu bar click on Sprache and select english. Maybe you can already see the aquaero screens but they will give you crazy values because the aquaero needs a newer firmware. Click on aquaero and select flash firmware. Choose the file 'aquaero firmware 410a.afd4'. You will see a info-box, just click OK. I'm not sure if you have to click something again, just read and do what it says. On the aquaero you have to press and hold the set button for 2-3 seconds and the update will start.
10.) When the update is finished the aquaero display says you have to restart. Shutdown windows and repeat step 7. Now you can reattach your senors and fans.
11.) Start your computer, in Windows start the aquasuite and welcome to the world of aquaero ;D