blank page on control panel options

Hi,several months ago I installed advanced guestbook for a website, I forgot about it, but now I saw that on admin panel, the options "private messages" and "easy admin" shows a blank page, the url of that pages is like this:

.../guestbook/admin.php?action=show&tbl=gb&session=a89b5eed3dd55bdf2288f6026871a04b&uid=1

If I press back shows a session expired page, but the rest of option showing correctly, what the reason for that?

thank you!

Somebody have an idea?, help me please

Try re uploading all the files again.