Program doesn't realize user name and/or password

I loaded the Advanced Guestbook and the report was that everything had loaded and it reported my username and password correctly. But when I tried to enter administration, I received an 'invalid" username and/or password. I don't understand this since the program reported everything correctly. I checked with my ISP help desk and they couldn't help. They advised to post here. I checked the previous posts and one post was about the same as mine and he was told to read some replies. I read those but couldn't find an answer to my question. Can anyone offer any suggestions and assistance with this problem. It must be something in the program. Thanks.

The answer is in the sticky thread titled READ THIS BEFORE POSTING ANY GUESTBOOK QUESTIONS

I have same problem

My GuesBook is on ;
http://billyidol.livenet.pl/AdvancedGuestBook
Please help me to loging in administration panel