Cannot redeclare class vbulletinhook

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Hi everyone. This is my first serious attempt at hacking vBulletin, so cut me some slack if this is basic. I keep getting this error in one of my scripts:

Fatal error: Cannot redeclare class vbulletinhook in /home/direcory/public_html/script.php on line 0

Basically I've got an index script which is calling two other scripts--both of them pull data from my forum. I can't seem to figure out whats causing this error--any suggestions?

Thanks.