The Fade mod, which I believe you're using, is the problem. According to the FAQ in its forum, "The Guarded Compound is temporarily locked for the moment - it becomes unlocked during Fades first quest. This is being amended for the actual proper V1 release."
http://chosenofmystra.net/forums/viewtopic.php?t=83
Add) I just reread your other post about your mage and Fade. If that first quest is meant to be the "mini-quest" that you mentioned, then I suppose that I should also give you directions to the entrance. Go to the rightmost street that runs north-south on your screen, the one that also borders the Radiant Hart. The entrance is on the upper part of the street to the right. Coordinates are (x=4204, y=2096). Press "x" to display the coordinates that your cursor is currently on.
Good luck.
[ 04-22-2006, 11:55 PM: Message edited by: Desuma Malevois ]