Problem with setup of domains on multisite


I have a problem on a multisite. For the sake of my client I will keep the URL anonymous here on this thread, however, I have granted you full access to the website, so you can take a look and maybe help me to find a solution to my issue.

Main Domain
My clients main domain is:

Second domain
My client also have a english version of her website, which is This domain is currently set to show the content of the root where is installed.

Domain mapping
I have used WPMU's domain mapping plugin ( OF COURSE :smiley: ) to add the .com domain to the english website, so that the content from is shown on

So far so good, it works as expected...

However, my client also have two other installations, and These installations she want to show using the .com domain, like this:

Now, I can't map those domains, and when I go to administrate the installs and change the URL manually ( see the screenshot ), and then load the page. I just get an 404 error.

Let me know if I need to clarify something here :smiley: