The CMS had been running fine for months, client tried to log in this morning and got the following error:

[NullReferenceException: Object reference not set to an instance of an object.]
   umbraco.BusinessLogic.Utils.TypeFinder.FindClassesOfType(Boolean useSeperateAppDomain) +27
   umbraco.BusinessLogic.Actions.Action.RegisterIActions() +71
   umbraco.BusinessLogic.Actions.Action..cctor() +150

[TypeInitializationException: The type initializer for 'umbraco.BusinessLogic.Actions.Action' threw an exception.]
   umbraco.BusinessLogic.Actions.Action.GetJavaScriptFileReferences() +0
   umbraco.cms.presentation._umbraco.RenderActionJS() +47
   umbraco.cms.presentation._umbraco.Page_Load(Object sender, EventArgs e) +1050
   System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) +14
   System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) +35
   System.Web.UI.Control.OnLoad(EventArgs e) +99
   umbraco.BasePages.BasePage.OnLoad(EventArgs e) +15
   System.Web.UI.Control.LoadRecursive() +50
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +627

Any ideas?

Unfortunately I don't have any access to the db to check log files.