What version of the game do you have (region)? There is a patch in the works for the non-US versions to bring them up to 1.03, though there haven't been any updates on its status (it may get delayed to combine the beta testing cycle with the add-on, to be released in August/September, since there are additional changes/fixes being made to the main game).
Did you try installing the game on the hard drive (if available, and if you haven't done so already)?
You do not need to defeat Raze; he drops a dragon skill book, a cuirass needed for Wesson (if you picked him as your enchanter) and Ulthring's Leggings (if you read Raze's mind). If you can not get in, you could miss the achievement for fully upgrading the battle tower, and would miss one for destroying all the flying fortresses, if you care about that.
I would suggest leaving it for now, and trying back later. If it was just a glitch, maybe if you do a bunch of other stuff and then return (at some point before heading to the hall of echoes) the headquarters could get loaded properly.
Did you contact the publisher, to see if this is a known issue in that version, and if there are any fixes or workarounds? The email address should be in the manual, or you could try Larian directly (support@larian.com).
