Thanks a lot for your replies, I'm always happy learning something new.
But, next issue... I've entered a passphrase with special characters, and neither with a German nor English keyboard it'll be accepted.
Error message "no key with this passphrase" is displayed every time I'm trying to enter it.
So I've re-installed another instance without special characters and it worked, finally.
For security reasons and in my opinion, special characters are state of the art and I'm really surprised that it seems to be, they can't be used in an encryption passphrase in this operating system.
As I see, there is much work to do for it.
Will it be safe upgrading from version 4.5.0 to 5 or will I've to install it all new?