I was moving a installation to a production server and was getting this error message: Notice: Undefined index: 0 in app/code/core/Mage/Core/Model/Mysql4/Config.php on line 92. It took alot of searching to figure out the problem, but here is what I found. When Magento installs it sets store and website ids in the database. When transferring the database the new database did not like having an id of 0 for the admin part of the site, so it made it have an id of 2. This is what my problem was. To fix it I went into the core_store and core_website Tables and gave the admin site an id of 0. It looks like this may only affect certain versions of magento(Earlier versions). Hope this helps someone else.

P.S. I also got foreign_key_constraint errors when importing my database. To solve this disable foreign key check when you export your database. Then when you need to change the core_store and core_website id’s you will probably need to surround your sql with the following code:

set foreign_key_checks=0;
//SQL to update ids
SET FOREIGN_KEY_CHECKS=1;

This Magento Error Message was giving me the hardest time. It seems to occur when you have a mis-match in your layout files.

What happend to me was I hard coded the newsletter into a page. In the newsletter layour file It was instructed to put the newsletter in the page also. This meant that it was included in the page more than once. That is why the error is thrown. Check your layout files to get a better grip on the problem.

I need to give thanks to Branko Ajzele for his post. It helped me realize what the problem was.

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