This isn't the same as "not one ATF agent came in that day." I teach at a university, and several professors aren't here today. That doesn't mean they were "tipped off" not to come in. It means they don't work today!
As for Shaw's comment, this is highly suspect. Did he see a pager that "told people not to come in?" Was it verified it came from the government? I'm highly suspicious of this entire line of thinking. I don't doubt that Iraq or AQ could be involved, but I don't buy people being 'warned' not to come to work.
Well, deconstruct all you like. I'm telling you that it was reported in the news that all the ATF field agents were absent from the building on the morning of the bombing. I heard that report myself. It may be in error, but I am not lying to you.