I was bashing my head into this brick wall for a couple days before I thought to disable the Simple Tagging plugin...
I was trying to create links to a tag archive and my tag archive page was blank. Not just one tag archive, but every tag archive. It was no different if I created a new tag.php or used the standard archive.php. I even tried using a wp_query thinking maybe something was broken with the loop for some reason. Nope. Tag archives just aren't there.
What I didn't do was go through the various configuration options extensively -- honestly, by the time I found that it was just a plugin, I was just happy to have my tag archives working again -- but I didn't see anything that applied to or seemed to affect the archive page at all.
Just thought I would throw that out there in case anyone else runs into this issue.