I was running into the same issues and didn’t find some of the steps I had to do. So for anybody else…
1. Delete the var directory and make a new one with permissions 777.
2. Go to the shell directory and issue the command php compiler.php disable
3. Go to the tmp directory, (/tmp) and delete all the Zend files and the magento directory.
4. Go to the data base and issue the SQL query:
SELECT * from core_config_data WHERE path IN (’web/unsecure/base_url’, ‘web/secure/base_url’, ‘admin/url/custom’);
Then change to the current URL.
5 .Go to the database and issue these SQL queries:
UPDATE core_config_data SET value = 0 WHERE path = ‘dev/js/merge_files’;
UPDATE core_config_data SET value = 0 WHERE path = ‘dev/css/merge_css_files’;
6. Don’t forget to set your shipping and credit cards to their live URLS and turn on email.
This seemed to do it for me.