Hi @Daniel Kastner 

thank you very much. Seems I had the same problem as you. 3.12.7 works like charm. 

Hi @Ashok Kumar, 
I still get the same error after editing both PythonRuntimeLibrary and PyhtonRuntimeLibraryVersion. 

He's the situtation:
Windows 11 x64
Installed 2024.1 first, then upgraded to 2024.3 developer preview version
C:\InterSystems\IRIS\lib\python\ folder is present with 9 files. (From the original 2024.1 installation) 
I then installed Python 3.13 and let the installer add the system path variable
set PythonRuntimeLibrary - C:\Program Files\Python313\python3.dll (also tried C:\Program Files\Python313\python313.dll)
PythonRuntimeLibraryVersion - 3.13

I tried renaming the lib\python\ folder to see if anything changed but no luck
\mgr\python is empty

when running python from windows itself, it works as expected

Restarted both IRIS and the whole machine couple of times while testing. 

Any ideas? 
Thanks

Thank you that helped stopping the processes although it took a couple hours for the processes to disappear