Old spambayes version (1.0.4) was used without problems for years (Win2000, XP, Win7, all with Outlook 2003).
Installing spambayes-1.1a6.exe works fine during installation process. Checkbox "converting database to 1.1" was allways checked,I tried installing spambayes for all Outlook users and just for my account.
When starting Outlook 2003 this message pops up:
There was an error initializing the SpamBayes addin
Please re-start Outlook and try again.