See http://resources.arcgis.com/content/patches-and-service-packs?fa=viewPatch&PID=17&MetaID=1857 for more information. This patch addresses multiple issues with spatial joins, including null output and crashes.
I recently was made aware of a fix for the long-present problem with ArcGIS on domain machines (i.e., users log in to lab or office machines using their ISO password) where a script error is generated every time a tool in ArcToolbox is opened. After dismissing three error dialog boxes, the tool will run ‘normally’. Not a fatal error, but annoying.
The problem stems from Internet Explorer, and can be fixed by replacing two files in \program files(X86)\ArcGIS10.0\ArcToolbox\Stylesheets
A description of the fix and the replacement files are available from http://support.esri.com/en/knowledgebase/techarticles/detail/38099
Administrator privileges are needed to implement the fix.