I was working with a client who wantedto redirect their blog from one domain to another, they has some issues with the process they used.
The Problem
At attempt to redirect the blog has been done byamending the site URL and the home page in the blog options within wordpress.
This redirected as expected, but it also prevented login to the site. When they tried to login to blog/wp-admin, they were redirected to newblog/wp-admin. This made the admin section of the blog unaccessible.
The Solution
It was down and dirty database edit time. I gained access to the hosting account and using phpmysqladmin I was able to edit the tables and revert back to the original blog URL and home page. I also noted that the .htaccess file had a redirect to the wrong directory, so I amended this also.
I installed the appropriate 301 redirection plugin and gave my client instructions on the best way to migrate domains.
If you want to redirect your blog I recommend leaving your old blog intact and using a 301 redirection plugin. I detail this in my case study post Migrating From One Domain to Another