Oshyan, I'm sorry to report that this bug is a bit more extensive than I first thought, is TG 2.0 specific, and is not connected with the specific terrain file. Having tried unplugging various aspects of the previous terrain, to no avail, I decided to create a test file from the default scene. All I did was generate the heightfield, stick a lake in, and move the camera to a suitable POV. I placed the sun behind the terrain first, and sure enough, the bright spots appear in the shadow (see basic-(test-lake).jpg) - N.B., this is with ray traced shadows enabled. Then I raised the sun just above the horizon, and there are still white spots in the terrain shadow.
The reason I can say this is TG2.0 specific is I ran this test file through the Beta (excellent decision not to overwrite this with the final release, by the way), and no spots were visible in either case (see attachments). The test file is also attached.
I should add that this problem wouldn't have been detected if I hadn't decided to make the lake completely smooth, as obviously any waves would completely mask these minor artifacts. I guess that makes it a minor bug, as most people won't be using completely smooth lakes. Is it possible this bug is connected with the new settings for the "Ray detail region"
I wouldn't know enough to fiddle with these settings to see if they might resolve it.