Suddenly we cannot unfold a certain node in the epitree. In our log file I can see the following message. Seems like some value is wrong in one of the pages, but I can't figure out which one. What value might cause this problem?

Using epi 4.61.3

Error in: http://www.bilia.se/secure/editor/EditTree.aspx?id=56792
Referrer: http://www.bilia.se/secure/editor/QuickSearch.aspx?mode=&id=
Error Message: Page "56797" has invalid data, cannot find either master language branch or loaded version
Stack Trace:
    at ᐚ.ᐁ()
   at ᐚ.InitializeData(ApplicationConfiguration config)
   at EPiServer.DataAccess.PageListDB.LoadList(PageReference pageLink)
   at EPiServer.DataFactory.ᐃ(PageReference )
   at EPiServer.DataFactory.ᐁ(PageReference )
   at EPiServer.DataFactory.GetChildren(PageReference pageLink, ILanguageSelector selector, AccessLevel access)
   at EPiServer.WebControls.ExplorerTree.GetChildren(PageReference pageLink)
   at EPiServer.PageTreeLoader.PreloadHasChildren(TreeState state, PageData page)
   at EPiServer.PageTreeLoader.ᐁ(TreeState , PageReference , Boolean , Int32 )
   at EPiServer.PageTreeLoader.ᐁ(TreeState , PageReference , Boolean , Int32 )
   at EPiServer.PageTreeLoader.ᐁ(TreeState , PageReference , Boolean , Int32 )
   at EPiServer.PageTreeLoader.ᐁ(TreeState , PageReference , Boolean , Int32 )
   at EPiServer.PageTreeLoader.ᐁ(TreeState , PageReference , Boolean , Int32 )
   at EPiServer.PageTreeLoader.GetPageTree(PageReference parent, PageReference[] openPages, IPageSource pageSource, Int32 nrOfLevels)
   at EPiServer.WebControls.PageTreeData.PopulatePages(PageDataCollection pages)
   at EPiServer.WebControls.PageControlBase.ᐁ()
   at EPiServer.WebControls.PageControlBase.GetPages()
   at EPiServer.WebControls.ExplorerTree.Render(HtmlTextWriter output)
   at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
   at System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
   at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
   at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
   at System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
   at System.Web.UI.WebControls.Label.RenderContents(HtmlTextWriter writer)
   at System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter writer)
   at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
   at System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
   at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
   at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
   at System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
   at System.Web.UI.WebControls.Label.RenderContents(HtmlTextWriter writer)
   at System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter writer)
   at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
   at System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
   at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
   at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
   at System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
   at System.Web.UI.HtmlControls.HtmlForm.RenderChildren(HtmlTextWriter writer)
   at System.Web.UI.HtmlControls.HtmlContainerControl.Render(HtmlTextWriter writer)
   at System.Web.UI.HtmlControls.HtmlForm.Render(HtmlTextWriter output)
   at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
   at System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
   at System.Web.UI.HtmlControls.HtmlForm.RenderControl(HtmlTextWriter writer)
   at ASP.secure_editor_edittree_aspx.__Render__control1(HtmlTextWriter __w, Control parameterContainer) in d:\WebApplications\Bilia\secure\editor\EditTree.aspx:line 146
   at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
   at System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
   at System.Web.UI.Page.Render(HtmlTextWriter writer)
   at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
   at System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
   at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
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