When ever I open the Skins page from admin or host I get this error

InnerException: Object reference not set to an instance of an object.
FileName:
FileLineNumber: 0
FileColumnNumber: 0
Method: DotNetNuke.UI.Skins.SkinDefaults..ctor
StackTrace:
Message: DotNetNuke.Services.Exceptions.ModuleLoadException: Object reference not set to an instance of an object. ---> System.NullReferenceException: Object reference not set to an instance of an object.at DotNetNuke.UI.Skins.SkinDefaults..ctor(SkinDefaultType DefaultType)at DotNetNuke.Common.Globals.get_DefaultSkin()at DotNetNuke.Modules.Admin.Skins.EditSkins.isFallbackSkin(String skinPath)at DotNetNuke.Modules.Admin.Skins.EditSkins.ProcessSkins(String strFolderPath)at DotNetNuke.Modules.Admin.Skins.EditSkins.ShowSkins()at DotNetNuke.Modules.Admin.Skins.EditSkins.LoadSkins()at DotNetNuke.Modules.Admin.Skins.EditSkins.Page_Load(Object sender, EventArgs e)--- End of inner exception stack trace ---

I used reflector and looked at the DotNetNuke.UI.Skins.SkinDefaults..ctor(SkinDefaultType DefaultType) it looks like it was trying to get the path from DotNetNuke.config file but this file is basically one big comment.. I am kinda lost on what to do at this point.

I think this is a problem relating to my "successful" update from 4.5 to 4.8.

No, both the Dnn Blue and Grey skins are still there, plus I just added a new portal that loaded the one by default.

My orginal search for this problem didnt find much but I finally found the answer.

Locate the following two functions inside the "Private Methods" Region

        Private Function isFallbackSkin(ByVal skinPath As String) As Boolean
            Dim strDefaultSkinPath As String = (Common.Globals.HostMapPath & SkinInfo.RootSkin + DefaultSkin.Folder).Replace("/", "\")
            If strDefaultSkinPath.EndsWith("\") Then
                strDefaultSkinPath = strDefaultSkinPath.Substring(0, strDefaultSkinPath.Length - 1)
            End If
            Return skinPath.IndexOf(strDefaultSkinPath, StringComparison.CurrentCultureIgnoreCase) <> -1
        End Function

        Private Function isFallbackContainer(ByVal skinPath As String) As Boolean
            Dim strDefaultContainerPath As String = (Common.Globals.HostMapPath & SkinInfo.RootContainer + DefaultSkin.Folder).Replace("/", "\")
            If strDefaultContainerPath.EndsWith("\") Then
                strDefaultContainerPath = strDefaultContainerPath.Substring(0, strDefaultContainerPath.Length - 1)
            End If
            Return skinPath.IndexOf(strDefaultContainerPath, StringComparison.CurrentCultureIgnoreCase) <> -1
        End Function

Replace the marked red text with: glbDefaultSkinFolder

This fixed my issue