Thank you for your interest in Syncfusion Products.
I have analyzed your posted issue in our side.
InvalidOperationException is thrown because of following reasons,
1. Method call is invalid for the object's current state.
2. Modifications of collections’ objects after the enumerator are created.
3. Resource set is closed before the method call is made.
The important part of the InvalidOperationException means is the Message property. The message says "Collection was modified" and that the enumeration won't work.
This is because you are changing the elements in the collection while looping over it.
To resolve that, please follow the steps,
1. Set the valid enumerator’s state
2. Add references to all the objects.
3. Iterating over the temporary collection.