Nice. It's interesting this error is in the skin page. But it looks like an error with some type of custom module or coding

Line: 187 is where your error actually is: 

tabParent = GetDnnTabByTabId(tabId) 

GetDNNTabByTabId() is not a function in DNN core and it looks like it's trying to get the current tabInfo object from the current TabId. My guess is that the function is unable to determine to the portal to get the correct TabInfo object so it returns null. So when it gets to line 189 it's trying to get the name of the tab but is unable to since the object is set to nothing.

Try going to that line and replace it with:

dim tc as new DotNetNuke.Entities.Tabs.TabController()
tabParent = tc.GetTab(tabId)

If it's still giving an error it's possible that tabId is null or 0. Or the page it is looking for simply does not exist in the database.

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Domain name is a very important part of how DNN determines the portal to load and how to create the Friendly URLs.

Again there appears to be some custom code and without knowing exactly what that function is doing it will be tricky to diagnose. At this point I would have to test it myself which if you are open too I would be willing to do.

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