I just applied the SSL certificate to the zen cart shop. I had to make several changes as it is described in the notes:
edited 2 configure.php files for catalog and for admin reflecting htpps:// in the links.
After it was done, I noticed that while customer is being successfully authenticated or just newly created, he/she is being returned back to login page with the message Please Login...
I don't know if it's related to SSL changes or to other customizations I have done before.

I would greatly appreciate for any clue!