To use mojoPortal multi site feature it needs to really run as a root web site not in a sub folder.
The problem is you have a strange web site configuration where sites are running in sub folders and you have some redirect from root to the sub folder. Probably some default page in the root is doing the redirect. If you created it you should be aware of it.
You need to learn more about IIS and you won't use these strange redirects, instead you will create multiple root sites in IIS and use host headers so they can all run on the same ip address. your current configuration is not good for many reasons, not only will it not work with mojoPortal multi sites but it is bad for SEO to have this redirect you are using.
I recommend watch the videos listed here:
and do some more reading to learn more about IIS configuration and correct ways of setting up web sites.
when you learn how to do it you will not have your sites running in sub folders like /defaultsite or /mojoportal, that is not a good way to do things.
instead you can have www.yourdomain.com for your non mojo site and something else like
cms.yourdomain.com for the first mojo site and any host name for other sites
Hope it helps,