The Facebook 1.5 app created a problem of duplicate calendar entries on my Blackberry. I thought deleting the application would fix it (I don’t really use Facebook much anyway), and at first it seemed like it did. But then more duplicate entries appeared. When I examined them in detail, they would show up as Facebook calendar entries. The link in the title shows what worked for me, post Facebook deletion:
If you want to totally delete the Facebook calendar then go into Options -> Advanced -> Service Books and delete Facebook [ICAL]
Many thanks to Crackberry forums user TheStoffer for this solution, for it seems to be working.