Quote - Im pretty sure that happens when you install a demo version of Vue, or when you don't license it, but it looks like an E-on watermark, and on your picture it doesn't look quite like it so im honestly puzzled...

 

i'd recommend deleting every single vue folder from your computer (even the licenses hidden within the program files folder of windows) and try reinstalling it.

 

Emmm...I think I found the problem.Not caused by what you guessed,actually I opened the "re-use indirect lighting"and then did some change to the scene,but forgot to re-render the radiosity map...so the old wrong indirect map matched the new scene,caused the strange problem :D

Hope my discovery can help somebody else who also met the same or similar problem:D