Original report was:
Right click on folder containing one or more encrypted files and select Decrypt or Decrypt and Verify. Request fails with message "Error returned by the GnuPG user interface: Invalid argument"
The idea here is that if you select a folder and then right click it for decryption, Kleopatra creates a list of the encrypted files in this folder (identified through gpgme_data_identify) and then asks the user if she really wants to decrypt them all. In case of yes, it would just start a job for each of the files like we already do if you e.g. switch into a folder and select all files and then decrypt them.