Crash on startup every time

Have been using sourcetree fine for some time and now it simply won't startup. Here's the call stack in the event log:

Application: SourceTree.exe
Framework Version: v4.0.30319
Description: The process was terminated due to an unhandled exception.
Exception Info: System.UnauthorizedAccessException
at Microsoft.Win32.RegistryKey.Win32Error(Int32, System.String)
at Microsoft.Win32.RegistryKey.SetValue(System.String, System.Object, Microsoft.Win32.RegistryValueKind)
at SourceTree.AppRoot.RegisterBrowserEmulationModeKey(System.String, System.String, UInt32)
at SourceTree.AppRoot.OnStartup(System.Windows.StartupEventArgs)
at SourceTree.App.OnStartup(System.Windows.StartupEventArgs)
at System.Windows.Application.<.ctor>b__1_0(System.Object)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(System.Delegate, System.Object, Int32)
at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(System.Object, System.Delegate, System.Object, Int32, System.Delegate)
at System.Windows.Threading.DispatcherOperation.InvokeImpl()
at System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object, Boolean)
at System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object, Boolean)
at System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object)
at System.Windows.Threading.DispatcherOperation.Invoke()
at System.Windows.Threading.Dispatcher.ProcessQueue()
at System.Windows.Threading.Dispatcher.WndProcHook(IntPtr, Int32, IntPtr, IntPtr, Boolean ByRef)
at MS.Win32.HwndWrapper.WndProc(IntPtr, Int32, IntPtr, IntPtr, Boolean ByRef)
at MS.Win32.HwndSubclass.DispatcherCallbackOperation(System.Object)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(System.Delegate, System.Object, Int32)
at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(System.Object, System.Delegate, System.Object, Int32, System.Delegate)
at System.Windows.Threading.Dispatcher.LegacyInvokeImpl(System.Windows.Threading.DispatcherPriority, System.TimeSpan, System.Delegate, System.Object, Int32)
at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr, Int32, IntPtr, IntPtr)
at MS.Win32.UnsafeNativeMethods.DispatchMessage(System.Windows.Interop.MSG ByRef)
at System.Windows.Threading.Dispatcher.PushFrameImpl(System.Windows.Threading.DispatcherFrame)
at System.Windows.Application.RunDispatcher(System.Object)
at System.Windows.Application.RunInternal(System.Windows.Window)
at SourceTree.App.Main()