In many portals (not in all) I get the "An item with the same key has already been added" critical error when I try to load the "site settings" or the "page settings" or the "page management" pages.

I noted this problem after the 7.3.0 and 7.3.1 upgrades (but I'm not sure that this was the cause)

Here an error example stack:

AssemblyVersion:7.3.1

PortalID:73

PortalName:RESIDENCE AZZURRA - Affitto, acquisto e vendita appartamenti turistici per vacanze nelle Dolomiti di Pozza di Fassa

UserID:1

UserName:host

ActiveTabID:3872

ActiveTabName:Pages

RawURL:/it-it/admin/pages.aspx

AbsoluteURL:/Default.aspx

AbsoluteURLReferrer:http://www.residenceazzurra.com/

UserAgent:Mozilla/5.0 (Windows NT 6.3; WOW64; rv:30.0) Gecko/20100101 Firefox/30.0

DefaultDataProvider:DotNetNuke.Data.SqlDataProvider, DotNetNuke

ExceptionGUID:396c05d1-adc3-4820-9618-d46f281d2b1c

InnerException:An item with the same key has already been added.

FileName:

FileLineNumber:0

FileColumnNumber:0

Method:System.ThrowHelper.ThrowArgumentException

StackTrace:

Message:

DotNetNuke.Services.Exceptions.PageLoadException: An item with the same key has already been added. ---> System.ArgumentException: An item with the same key has already been added.
   at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource)
   at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)
   at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer)
   at DotNetNuke.Web.UI.WebControls.DnnSkinComboBox.OnLoad(EventArgs e)
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
   --- End of inner exception stack trace ---

Source:

Server Name: INSOTECWEB