I just ran across an error transferring a Magento site from one host to another and wanted to share the solution here. The fix is fairly simple however the debug process to track down the fix was quite involved.

The Problem:

After an export/import of the Magento database I ran into the following two errors when trying to access the site.

The first error I ran into after moving the site was the following:

Notice: Undefined index:  0 in/app/code/core/Mage/Core/Model/Mysql4/Config.php on line 88 

The solution:

The solution to this error was to add the following two lines to the top of my sql import file.

SET FOREIGN_KEY_CHECKS = 0 ;
SET SESSION SQL_MODE="NO_AUTO_VALUE_ON_ZERO";

The first line fixes a common issue with Magento when trying to export/import databases where you get an error about foreign constraints.

The second line fixes  an issue where associative id's are automatically changed by MySQL which breaks the association.The specific values that get changed and cause this error are:

Table = core_store | Values = store_id & website_id
The correct values are: 
	
		
			
store_id
			
code
			
website_id
			
group_id
			
name
			
sort_order
			
is_active
		
	
	
		
			
0
			
admin
			
0
			
0
			
Admin
			
0
			
1
		
		
			
1
			
default
			
1
			
1
			
Default Store View
			
0
			
1
		
	

Table = core_website | Values =  website_id 
The correct values are: 
	
		
			
website_id
			
code
			
name
			
sort_order
			
default_group_id
			
is_default
		
	
	
		
			
0
			
admin
			
Admin
			
0
			
0
			
0
		
		
			
1
			
base
			
Main Website
			
0
			
1
			
1
		
	

Basically the website_id column in core_store must match thewebsite_id column in core_website and the store_id for admin in core_store must be 0. 

The Second Problem:

After fixing the first issue I ran into a second error message as follows:

Recoverable Error: Argument 1 passed to Mage_Core_Model_Store::setWebsite() must be an instance 
of Mage_Core_Model_Website, null given, called in... ...app/code/core/Mage/Core/Model/App.php on 
line 341 [0] in Mage_Core_Model_Store->setWebsite(NULL) in...

The Second Solution:

This is because the id's from the first issue where cached so in short... delete everything in var/cache/ and you should be home free!