Adobe Air fails to install

After encountering difficulties with an app running under Air, I wanted to reinstall Adobe Air. Big mistake. Now I can't reinstall it ... I keep getting the same error code.

I am running a Win10 64 system with full administrator rights.

The log reads like this:

[2020-02-03:21:53:17] Runtime Installer begin with version 32.0.0.125 on Windows 10 x86
[2020-02-03:21:53:17] Commandline is:
[2020-02-03:21:53:17] No installed runtime detected
[2020-02-03:21:53:20] Relaunching with elevation
[2020-02-03:21:53:20] Launching subprocess with commandline c:\users\erb\appdata\local\temp\air900f.tmp\adobe air installer.exe -ei
[2020-02-03:21:53:20] Elevated install failed: returned error code -1
[2020-02-03:21:53:20] Exiting due to error: [ErrorEvent type="error" bubbles=false cancelable=false eventPhase=2 text="Launching elevated sub-installer failed" errorID=5100]
[2020-02-03:21:53:22] Runtime Installer end with exit code 7

I hope somebody can help me get air running again.