Why do I get "no keys for decryption found" when trying to use a definitely valid keyring?
First, ensure that you have set the license key.
Next, check that you specify correct private keyring.
If your keyring or a key uses a password, and the key contains subkeys, then subkeys' Password must also be set. Common mistake is to copy OnKeyPassphrase event handler from the sample code, and not to add the handler to the OnKeyPassphrase event (using += operator in C#). Another mistake is that the keyring is not loaded from the disk for some reason (wrong folder name specified etc.). Always check that the keyring *does* contain the keys.