Multiple reports of the Layouts page editor not allowing users to scroll have been posted to the Blogger Help Groups recently. Blogger has reported the issue resolved as of today. Clear your browser's cache (ctrl + f5 on a PC), close your browser, then re-open it and login to your blog. Please report any continuing issues to http://knownissues.blogspot.com
There does seem to be an unofficial limit on how many page elements you can stuff into a sidebar or other section of a template before it breaks the visibility of the Layouts tab screen.
Why can't I scroll my Layouts screen?
Blogger code issues - There was an issue with the scrollbars that was fixed today. The knownissues.blogspot.com blog had the following update:--------------------
Nevertheless, we encourage template designers to use the
body#layout
CSS selector to add CSS styles that adapt templates to the editor.Update, 2/29: The Layouts editor now expands to the size of the template.
Browser updates can cause temporary problems
It can be related to how different browsers display information. IE6 appears to display a full scrollbar, while recent updates to FireFox seem to be causing display issues. Find out how to compress your layout
Custom Templates may break the Layout Editor
Making custom changes to your blog template can cause issues with the layout editor. Blogger controls the layout and look of the administration screens using CSS. Be careful when adding new CSS styles or code to your template.