I am getting this error - I understand this to be a fault with a loop somewhere that is changing the list while iterating over it. I am able to ignore the error and continue editing the modeller and using the application, but I would obviously rather fix it before I continue upgrading towards 5.19. Anyone help? (thanks for your help on my earlier question Gaurav) System.InvalidOperationException: Collection was modified; enumeration operation may not execute. at System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource) at System.Collections.Generic.List`1.Enumerator.MoveNextRare() at System.Collections.Generic.List`1.Enumerator.MoveNext() at System.Linq.Enumerable.<selectmanyiterator>d__1`2.MoveNext() at System.Linq.Enumerable.<selectmanyiterator>d__1`2.MoveNext() at Mendix.Modeler.Storage.Operations.TypeWalk.<getallstorageobjects>d__12.MoveNext() in c:\jenkins\workspace\AppStudio-Modeler\src\Mendix.Modeler.Storage\Operations\TypeWalk.cs:line 59 at System.Linq.Enumerable.<selectmanyiterator>d__1`2.MoveNext() at Mendix.Modeler.Storage.Operations.TypeWalk.<getallstorageobjects>d__12.MoveNext() in c:\jenkins\workspace\AppStudio-Modeler\src\Mendix.Modeler.Storage\Operations\TypeWalk.cs:line 59 at System.Linq.Enumerable.<selectmanyiterator>d__1`2.MoveNext() at Mendix.Modeler.Storage.Operations.TypeWalk.<getallstorageobjects>d__12.MoveNext() in c:\jenkins\workspace\AppStudio-Modeler\src\Mendix.Modeler.Storage\Operations\TypeWalk.cs:line 59 at System.Linq.Enumerable.<castiterator>d__1`1.MoveNext() at Mendix.Modeler.DataStorage.DataSets.DataSet.Check(IProblemsInfo problems) in c:\jenkins\workspace\AppStudio-Modeler\src\Mendix.Modeler.DataStorage\DataSets\DataSet.cs:line 113 at Mendix.Modeler.Common.GenericProjectCheckWorker.DoWork(ICheckable checkable) in c:\jenkins\workspace\AppStudio-Modeler\src\Mendix.Modeler.Core\Common\Problems\GenericProjectCheckWorker.cs:line 20 at Mendix.Modeler.Storage.StorageUtil.<>c__DisplayClass4`1.<foreachstorageobjectdo>b__3(IStorageObject a) in c:\jenkins\workspace\AppStudio-Modeler\src\Mendix.Modeler.Storage\StorageUtil.cs:line 106 at Mendix.Modeler.Storage.Operations.TypeWalk.ForEachObjectDo(IStorageObject root, Func`2 work, Boolean skipExcludedObjects) in c:\jenkins\workspace\AppStudio-Modeler\src\Mendix.Modeler.Storage\Operations\TypeWalk.cs:line 87 at Mendix.Modeler.Storage.Operations.TypeWalk.ForEachObjectDo(IStorageObject root, Func`2 work, Boolean skipExcludedObjects) in c:\jenkins\workspace\AppStudio-Modeler\src\Mendix.Modeler.Storage\Operations\TypeWalk.cs:line 92 at Mendix.Modeler.Storage.Operations.TypeWalk.ForEachObjectDo(IStorageObject root, Func`2 work, Boolean skipExcludedObjects) in c:\jenkins\workspace\AppStudio-Modeler\src\Mendix.Modeler.Storage\Operations\TypeWalk.cs:line 92 at Mendix.Modeler.Storage.Operations.TypeWalk.ForEachObjectDo(IStorageObject root, Func`2 work, Boolean skipExcludedObjects) in c:\jenkins\workspace\AppStudio-Modeler\src\Mendix.Modeler.Storage\Operations\TypeWalk.cs:line 92 at Mendix.Modeler.Storage.Operations.TypeWalk.ForEachObjectDo(IStorageObject root, Func`2 work, Boolean skipExcludedObjects) in c:\jenkins\workspace\AppStudio-Modeler\src\Mendix.Modeler.Storage\Operations\TypeWalk.cs:line 92 at Mendix.Modeler.Storage.Operations.TypeWalk.ForEachObjectDo(IStorageObject root, Func`2 work, Boolean skipExcludedObjects) in c:\jenkins\workspace\AppStudio-Modeler\src\Mendix.Modeler.Storage\Operations\TypeWalk.cs:line 92 at Mendix.Modeler.Storage.StorageUtil.ForEachStorageObjectDo[T](IStorageObject obj, Func`2 action, Boolean skipExcludedObjects) in c:\jenkins\workspace\AppStudio-Modeler\src\Mendix.Modeler.Storage\StorageUtil.cs:line 106 at Mendix.Modeler.Common.DefaultStorageObjectVisitor.ForEachStorageObjectDo[T](IStorageObject root, IStorageObjectVisitorWorker`1 worker, Boolean skipExcludedObjects) in c:\jenkins\workspace\AppStudio-Modeler\src\Mendix.Modeler.Core\Common\Problems\GenericProjectCheck.cs:line 57 at Mendix.Modeler.Common.GenericProjectCheck.Check(IProject project, IProblems problems) in c:\jenkins\workspace\AppStudio-Modeler\src\Mendix.Modeler.Core\Common\Problems\GenericProjectCheck.cs:line 29 at Mendix.Modeler.Common.Problems.Check(IProject project) in c:\jenkins\workspace\AppStudio-Modeler\src\Mendix.Modeler.Core\Common\Problems\Problems.cs:line 92 at Mendix.Modeler.Common.BackgroundChecker.DoCheck() in c:\jenkins\workspace\AppStudio-Modeler\src\Mendix.Modeler.Core\Common\Problems\BackgroundChecker.cs:line 106 at Mendix.Modeler.Common.BackgroundChecker.Check() in c:\jenkins\workspace\AppStudio-Modeler\src\Mendix.Modeler.Core\Common\Problems\BackgroundChecker.cs:line 73