Your guestbook maybe full. You will need to free up space in your guestbook before visitors can sign your again.
To free up some space in your guestbook, you may do any of the following.
Select the posts you would like to delete and click the Finished button. If you wish, you can also preserve past posts by creating an archive. Click the Archive button to create an HTML file containing all of your current posts, which you can then point your visitors toward so they can view older posts. Just remember: When you create an archive of your current posts, you'll still need to go back and delete any posts you no longer want to appear in your guestbook.
Note: If the link to "Approve Submissions" does not show up, you may have not selected this option when you setup your guestbook. To select this option, click "Guestbook Setup" at:
http://au.geocities.yahoo.com/gb/
Scroll down the page to "Step 8: Options." And check the box to "Review entries before posting."