I tested to remove the object in the trash bin one by one, and for on of the objects I got this error:

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.]
   EPiServer.DataAccess.PageLoadDB.LoadPageInternal(PageReference pageLink, Int32 languageBranchId, IDataReader reader) +1195
   EPiServer.DataAccess.<>c__DisplayClass1.<LoadPage>b__0() +304
   EPiServer.DataAccess.<>c__DisplayClass1`1.<Execute>b__0() +202
   EPiServer.DataAccess.DatabaseFactory.Execute(Action`1 method) +73
   EPiServer.Core.<>c__DisplayClass4.<GetPageInternal>b__3() +148
   EPiServer.Core.OptimisticCache`1.Read(String cacheKey, ReadAndCacheObject`1 readAndCacheObject) +1249
   EPiServer.Core.PageProviderBase.GetPageInternal(PageReference pageLink, ILanguageSelector selector) +830
   EPiServer.DataFactory.GetPage(PageReference pageLink, ILanguageSelector selector) +443
   EPiServer.ChangeLog.ChangeLogTracker.PreparePageDeleteLog(PageEventArgs args) +131
   EPiServer.PageEventHandler.Invoke(Object sender, PageEventArgs e) +0
   EPiServer.Core.PageStoreBase.RaisePageEvent(Object key, IList`1 pageLinks, PageEventArgs eventArgs) +221
   EPiServer.DataFactory.Delete(PageReference pageLink, Boolean forceDelete, AccessLevel access) +480
   EPiServer.UI.Edit.DeletePage.Delete_Click(Object sender, EventArgs e) +335
   EPiServer.UI.WebControls.ToolButton.RaisePostBackEvent(String eventArgument) +254
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +3691

I solved the problem by executing a sql query deleting the page:

exec  editDeletePage 3807