llegrand, Iv'e got the fix. 

1. Log into your database and go to the "ab_block_templates" table.

2. Find the row entry you want to show up in the block list.
(In your case it's "blocks/breadcrumbs.tpl")

You'll notice in the column "parent_block_id" some of the values are set at zero. This column enables the blocks so you can choose them from the "Adding block to section" screen or the plus sign. The "parent_block_value" determines where the block will be made available.

3. Edit the row entry "blocks/breadcrumbs.tpl" and set the value of "parent_block_id" to "1".

4. Go to "System/Cache" in your carts admin section and clear the cache.

5. Go back to "Design/Layouts/" in your admin and either click on an empty block in the "header" section or the plus sign. You'll now be given the option to add the bredcrumbs to that section.

I don't know what all the available values are for the "parent_block_id" column, but do know when I set the row "blocks/breadcrumbs.tpl" to "1" it was available for the header section.

I'm going to assume the available values for the "parent_block_id" are 1 thru 8 because there are eight sections in the layout panel. You'll have to experiment to see if it works that way.

I did notice in the "ab_block_templates" table there were multiple rows that shared the same template name but had different "parent_block_id". I assume this was so a specific block could be used in multiple parts of the layout.

Hope this helps you.

The solution I posted is not any sort of hack. The way the layout and blocks currently work is to keep novices from placing blocks in places that they won't fit or would look bad.

However, AbanteCart failed to set the values for the blocks they placed in the default installation layout to a value that would allow them to be restored if they were to be deleted by a user from the admin. Not so much a bug but a mistake made by AbanteCart.

All they have to do to fix the issue is to change the values in the MySQL file in the installation directory.

Seems like this is an issue that needs to be addressed. AbanteCart provided the block so users could easily login or create an account. If you delete the block and want to add it back later, you can't. This is obviously a bug. Not everyone has the experience to edit MySQL databases.

I noticed this issue also applies to the donate block. Why are these blocks available then unavailable after you delete them from the layout?

Thanks