I just looked at the webmap in IE and 29,5 is an Asteroid Base 3 - I suspect that NW assault mission may be allergic to that planet type.
(P.S, ack, the fonts on the webmap look gawdaful in IE, too big, that must be rectified, everone install Firefox 1.5... lol, I'll fix the fonts anyway... and IE seems dreadfully slow compared to Firefox...)