I finally found a way to "fix" it, but does not work all the time~~~
In my asp.net application, in the bin folder, there are a couple of dll components. After I cut all of them and paste to a safe place, the Website Data Source window will be back in functioning, at least showing the "your project has no data source" information. Then I restore the dll files one by one. After restoring each dll file, I will refresh the Website Data Source window to see if it is still working, until the time it doesn't, then the dll file is the suspect that "spoiled" the Website Data Source window.
Then I will have to scan through all the codes in that component by commenting/uncommneting the codes, and refreshing the Website Data Source window, to catch the codes that "spoiled" the window.
Finally, try to change the suspect codes to work in a different way until the Website Data Source window works, say, changing the return value type of a Function from a custom business object type, to a general Object type.
I was very happy that I solved this problem, until the same problem happened again...
A different suspect dll file was caught. And I have to repeat everything... It's ok still quite ok for me to do this since the codes are still little, but I can't imagine that I still need to do all these when I completed the whole project.
This problem is just so random...
Is this a bug or something in Visual Web Developer add-in report control? Anyone any idea?