Hi,
When clicking ‘Register’, the Platform Manager runs the Prepar3D.exe with some command lines so that Prepar3D does all the necessary entries in the config files itself. Unfortunately, there’s no feedback from the Prepar3D.exe when things don’t work.
So for P3D v4.4, the config file in question is the ‘add-ons.cfg’ located at C:\ProgramData\Lockheed Martin\Prepar3D v4.
If this one got somehow corrupted, then Prepar3D.exe is not able to add the SODE entry to it.
Can you upload that file here?