We're upgrading from Umbraco 10.8.3 to 13.2.0 and we have NewsletterStudio package in our solution.

We upgraded all files and packages, including NS.Core and NS from 10.0.15 to 13.0.6 (we also tried to 13.0.0).

Upon the db upgrade we received a NS error (see below) but all other CMS and packages upgraded fine.

However, when we try to send a NS email we received the same error we got upon the db upgrade:

System.AggregateException: One or more errors occurred. (An item with the same key has already been added. Key: NewsletterStudio.TransactionalEmailPicker) ---> System.ArgumentException: An item with the same key has already been added. Key: NewsletterStudio.TransactionalEmailPicker at System.Collections.Generic.Dictionary2.TryInsert(TKey key, TValue value, InsertionBehavior behavior) at System.Collections.Generic.Dictionary2.Add(TKey key, TValue value)
at System.Linq.Enumerable.ToDictionary[TSource,TKey](IEnumerable1 source, Func2 keySelector, IEqualityComparer1 comparer) at Umbraco.Cms.Infrastructure.Migrations.PreMigration.DataTypeSplitDataCollector.Handle(UmbracoApplicationStartedNotification notification) at Umbraco.Cms.Core.Events.INotificationHandler1.Handle(IEnumerable1 notifications) at Umbraco.Cms.Core.Events.NotificationHandlerWrapperImpl1.<>cDisplayClass002.<Handle>b__2(IEnumerable1 handlerNotifications) at Umbraco.Cms.Core.Events.EventAggregator.PublishCore[TNotification](IEnumerable1 allHandlers, IEnumerable1 notifications) at Umbraco.Cms.Core.Events.NotificationHandlerWrapperImpl1.Handle[TNotification,TNotificationHandler](IEnumerable1 notifications, ServiceFactory serviceFactory, Action2 publish) at Umbraco.Cms.Core.Events.EventAggregator.PublishNotifications[TNotification,TNotificationHandler](IEnumerable1 notifications) at Umbraco.Cms.Core.Events.EventAggregator.Publish[TNotification,TNotificationHandler](IEnumerable`1 notifications) at Umbraco.Cms.Core.Events.EventAggregator.Publish[TNotification](TNotification notification) at Umbraco.Cms.Infrastructure.Runtime.CoreRuntime.221()
at System.Threading.CancellationTokenSource.Invoke(Delegate d, Object state, CancellationTokenSource source) at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state) --- End of stack trace from previous location --- at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.CancellationTokenSource.ExecuteCallbackHandlers(Boolean throwOnFirstException) --- End of inner exception stack trace ---
at System.Threading.CancellationTokenSource.ExecuteCallbackHandlers(Boolean throwOnFirstException) at Microsoft.Extensions.Hosting.Internal.ApplicationLifetime.NotifyStarted()

This might be specific to our NS setup, although we do not know where to look for the duplicates (as per the error message) to fix them.

Any clue what's NewsletterStudio.TransactionalEmailPicker and where to to potentially fix it?

Thanks