Cannot open new Edit window (ctrl N) (4270486)

Selecting new edit window (ctrl-N) gives a System.MissingMethodException error. This started recently and now no queries, stored procedures, etc. can be opened.

System.MissingMethodException: Method not found: 'Void DevExpress.XtraGrid.Views.Grid.GridView.add_CustomSummaryCalculate(DevExpress.Data.CustomSummaryEventHandler)'.

Stack trace:

   at Quest.Toad.Grid.ToadGridControl..ctor()
   at Quest.Toad.ScriptResults.ScriptResultsGridControl.AddGridControl()
   at Quest.Toad.ScriptResults.ScriptResultsGridControl.ForceCreateGrid()
   at Quest.Toad.ScriptResults.ScriptResultsGridControl..ctor(Boolean delayGrid)
   at Quest.Toad.ScriptResults.ScriptResultsControl.addGridControl()
   at Quest.Toad.ScriptResults.ScriptResultsControl..ctor(IConnection conn)
   at Quest.Toad.Editor.EditorForm.CreateScriptResultControl()
   at Quest.Toad.Editor.EditorForm.CreateDockWindows(TabbedMdiWindow window)
   at Quest.Toad.Editor.EditorForm..ctor()
   at Quest.Toad.Editor.EditorForm.NewEditorForm()
   at Quest.Toad.SqlServer.Common.ScriptUtils.OpenScriptInEditor(String script, IConnection iconnection, String database)
   at Quest.Toad.SqlServer.Common.ScriptUtils.OpenScriptInEditor(String script, ITrl itrl)
   at Quest.Toad.SqlServer.Common.ScriptUtils.OpenScriptInEditor(StringBuilder sb, ScriptOptions scriptOptions, ITrl itrl)
   at Quest.Toad.SqlServer.Common.ScriptUtils.OpenScriptInEditor(StringBuilder sb, ScriptOptions scriptOptions, ITrl itrl, String editorCaption)
   at Quest.Toad.SqlServer.ActionHandler.Scripting.ScriptingActions.<>c__DisplayClass1b`2.b__19()