Decrypt object throws error when no passphrase is present

1) I have tried adding the parameter but it has not made any difference and I can't see any output being produced

Since you are not able to find the log file you can try saving it into a specific folder
Instead of ">log.txt" you can use ">c:\temp\log.txt"

2) Another thing you can try is to log in using the same user you use to run the agent.

For example, you are running an agent using an account called JohnSmith.
Login into windows as JohnSmith.
Open a command line and execute the command you see in the log
This might give you an idea of what is going on


3) Could you answer my second question from above, please? How does AETLE know where to look for the decryption key?

AETLE does not know anything about the decryption key and it does not look for the decryption key.
AETLE is using a third-party tool called Gpg4Win for decryption /encryption.
Gpg4Win is not a part of AETLE setup.
It is downloaded, installed and configured separately
Gpg4Win has it' own website and documentation
www.gpg4win.org/doc/en/gpg4win-compendium.html
This page talks about exporting and importing keys
www.gpg4win.org/doc/en/gpg4win-compendium_25.html