Tuan,
This has been a consistent issue. It was briefly fixed, by briefly I mean it seemed to work last week, and stopped working this week. However, the nature of the error has changed. Prieviously it would tell me the data was already loaded, and wouldn't give me the option to replace it. Now it gives me a phony error stating that the Object reference not set to an instance of an object. This would indicate a relationship problem with one of the lookup tables. This is not the case. I recieved the same error on every single one of my reports when I try to publish them, and the fix for each is the same. Switch my account to the same account and select publish again. I will then recieve a popup with the option to replace the existing data and it publishes just fine.
Matthew