Iec081 - DataType Attribute can only be used on methods if they are User methods or Function methods in FunctionContainer
The attribute [DataType] may only be used on methods if they are [User] methods or [Function] methods inside a class with [FunctionContainer] attribute.
You can also use the provided automatic Code Fix to remove the attribute or put it on the class if it is currently on a [Execution] __Process method of a class with a [Function] attribute. ( Press Alt + Enter on the Error line to find the Code Fix in the context menu)
Remove the attribute.
