Our Umbraco instance was working just fine and all of a sudden we're getting this error:

Server Error in '/' Application. Object reference not set to an instance of an object. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:

[NullReferenceException: Object reference not set to an instance of an object.] umbraco.editorControls.tinyMCE3.TinyMCE..ctor(IData Data, String Configuration) +457

[ArgumentException: Incorrect TinyMCE configuration. Parameter name: Configuration] umbraco.editorControls.tinyMCE3.TinyMCE..ctor(IData Data, String Configuration) +5856 umbraco.editorControls.tinyMCE3.tinyMCE3dataType.get_DataEditor() +123 umbraco.controls.ContentControl.addControlNew(Property p, TabPage tp, String Caption) +145 umbraco.controls.ContentControl.CreateChildControls() +867 System.Web.UI.Control.EnsureChildControls() +189 umbraco.controls.ContentControl.OnInit(EventArgs e) +123 System.Web.UI.Control.InitRecursive(Control namingContainer) +186 System.Web.UI.Control.AddedControl(Control control, Int32 index) +189 umbraco.cms.presentation.editContent.OnInit(EventArgs e) +1007 System.Web.UI.Control.InitRecursive(Control namingContainer) +186 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +2098