I don't know the answer to the problem with the trial, but I do know that
when I was browsing through the Expression Web forum and this forum last
night, I saw quite a lot of posts having to do with problems with the trial
version. One person even tried to contact Microsoft about it, but the answer
apparently was that they do not support the trial version.
My guess is that the trial version is buggy, and there may not be anything
we can do about it.