Re: I just refreshed from SVN but..
I'm not sure why you are getting that error. Maybe the siteSettings object is null for some reason. You could set a break point at line 1290 and stop the code at that point and check if siteSettings is null.
If it is null then set a breakpoint in Global.asax.cs line 79 and start again, then use F11 to step into where it creates siteSettings and see what if anything goes wrong.
siteSettings is created in Application_BeginRequest and then is stored in the HttpContext so it can be used anywhere in code for the rest of the request, so SiteSettings.GetCurrent is just getting a reference out of the HttpContxt but it will return null if siteSetting is not in HttpContext
Anyway those are the steps I would take to troubleshoot the problem if it were happening on my machine.
Hope it helps,