New Domains are not being mapped

On my network I have one domain that is being mapped to its' proper domain. It was first mapped months ago. Now I want to map another domain for another subsite. After entering it into the custom field under tools>domain mapping, saving it, and clicking on the link to the mapped domain, I'm taken to the wp-signup page of the main site of the network. ( /wp-signup.php? )

I don't know why this is happening. Any help would be appreciated.

Also, if it helps, I'm using version of the domain mapping plugin.

[This is a seperate issue: Automated update through the WPMU dashboard fails ("Could not remove the old plugin."). Everytime I update it manually through FTP by deleting the old folder, and replacing it with the new, along with the new sunrise file, my server hangs. The Apache process starts to consume 80-90% of the CPU. Error log reports bad queries.]