My problem is, the DNN is installed as a virtual directory, say root/dnn, meanwhile another asp.net application is installed in another virtual directory, root/app2. I make a new page in DNN and want it link to the app2. I select the "Link Url" as URL(A link to an external resource), and type in "/app2" as location. It is not working. DNN will automatically add http:// in front of it. I prefer to see http://domain added. But I don't know why. If I am using "~/app2", it looks DNN will add http://domain/dnn in front of it, makes it looks as app2 is a sub directory of dnn itself.

Hopefully, I explain my problem clearly. Any solutions? Thanks in advance.

Thanks Mart'n. Yes as you said, if I am using full name it will be ok. But it gives me another problem. Now, I am developing the website, so all works are done in my local computer. In this case, I can use full name "http://localhost/app2. in the future, when I put my website online, I need change http://localhost/app2 to http://real_domain/app2. If I am change the domain name, I need to do the same thing again. It doesn't make any sense to me. In a webpage, "/" means the root, the browser can automatically add server's domain in front of it. Actually, I don't know why DNN can't just keep relative path instead of adding "http:".