Oh and other thing before you screw ur self, make sure that you scene root looks execatly like they show in the explanation, capital letters and evrything, so rootpoint doesnt have any capitals but all the PXXX- have capital P otherwsie it wont export the null point to mesh. the name of the model doesnt matter, so good luck.

Actualy I managed to reproduce ur error recently, for one, when you export .XSI make sure to deselect everthing (Shift+ctrl+a), having something selected can couse convertXSI to give u that problem later, especialy if had a null point selected. The other thing make sure that in command prompt when converting you type in the names exactly for example: convertxsi judgment.xsi judgment.mesh
And are u following the right directions, here is a good tutorial made by cannadaman
http://files.filefront.com/convertxsi+stepsdoc/;11034555;/fileinfo.html

Im trying to think of what else to say. on when you go to documentation that tells u how to export to XSI got to figure 1g-2 on page 15 (its the bottom one) and make sure that all of ur export settings are like theirs. Hope this helps.

No problem and have fun. or curse ur self to hell. if u want to check what ur model looks like in game just replace it with a scout firgate, or something should give u a good idea of what ur model looks like.