The strange error i have mention before just happened again:
The text in the blue window is this:
 System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
   at System.Collections.ArrayList.ArrayListEnumeratorSimple.MoveNext()
   at System.Windows.Data.CollectionView.PlaceholderAwareEnumerator.MoveNext()
   at System.Linq.Enumerable.<OfTypeIterator>d951.MoveNext()
   at System.Linq.Enumerable.Contains[TSource](IEnumerable1 source, TSource value, IEqualityComparer1 comparer)
   at System.Linq.Enumerable.Contains[TSource](IEnumerable1 source, TSource value)
   at AcManager.Controls.ViewModels.AcObjectListCollectionViewWrapperBase1.RefreshFilter(AcItemWrapper obj)
   at AcManager.Controls.ViewModels.AcObjectListCollectionViewWrapperBase1.OnWrapperValueChanged(Object sender, WrappedValueChangedEventArgs e)
   at AcManager.Tools.Lists.AcWrapperObservableCollection.OnItemValueChanged(Object sender, WrappedValueChangedEventArgs e)
   at AcManager.Tools.AcManagersNew.AcItemWrapper.set_Value(AcPlaceholderNew value)
   at AcManager.Tools.AcManagersNew.BaseAcManager1.<EnsureWrapperLoadedAsync>d__60.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at AcManager.Tools.AcManagersNew.BaseAcManager1.<GetByIdAsync>d64.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at AcManager.Tools.AcManagersNew.BaseAcManager`1.<AcManager-Tools-AcManagersNew-IAcManagerNew-GetObjectByIdAsync>d67.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at AcManager.Pages.Windows.MainWindow.<OnNewLatestVersion>d90.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.AsyncMethodBuilderCore.<>c.<ThrowAsync>b__6_1(Object state)
   at System.Threading.QueueUserWorkItemCallback.WaitCallback_Context(Object state)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem()
   at System.Threading.ThreadPoolWorkQueue.Dispatch()
   at System.Threading._ThreadPoolWaitCallback.PerformWaitCallback()
Also after closing the blue window comes the windows error window(if it helps to solve the problem) that says:
Problem signature:
  Problem Event Name:	CLR20r3
  Problem Signature 01:	Content Manager.exe
  Problem Signature 02:	0.8.2245.37760
  Problem Signature 03:	5ff8aed4
  Problem Signature 04:	mscorlib
  Problem Signature 05:	4.8.4069.0
  Problem Signature 06:	5dc614b0
  Problem Signature 07:	6c95
  Problem Signature 08:	22
  Problem Signature 09:	System.InvalidOperationException
  OS Version:	6.1.7601.2.1.0.256.48
  Locale ID:	2057
  Additional Information 1:	0a9e
  Additional Information 2:	0a9e372d3b4ad19135b953a78882e789
  Additional Information 3:	0a9e
  Additional Information 4:	0a9e372d3b4ad19135b953a78882e789
Read our privacy statement online:
  http://go.microsoft.com/fwlink/?linkid=104288&clcid=0x0409
If the online privacy statement is not available, please read our privacy statement offline:
  C:\Windows\system32\en-US\erofflps.txt
Please fix this error.