I installed it on my test website and the installation went fine. Yesterday evening I was a bit to enthusiastic and installed it on the live website instead of the test website...

So, there must be something with one of the other mods on my live website which caused the errors..... maybe....
1. Pretty URLs Reverter 0.9.1
2. Custom Fields On Memberlist
3. Sitemap 2.0.0
4. Latest Members RC1 1.1
5. SMF Gallery Pro Recent Profile Images 1.0
6. PortaMx v0.956 0.956
7. SMF 1.0.17 / 1.1.9 / 2.0 RC1 Update 1.0
8. PortaMx v0.957 Rev1 0.957r1
9. Prettier_Quotes 1.12
10. Stop Spammer 2.2
11. Global Headers Footers 2.0
12. Internal_Links_Use_Same_Window 1.2
13. Ad Managment 2.3.4
14. Downloads System Pro 1.0.4
15. PortaMx v0.957 Rev2 0.957r2
16. Users Online Today 1.5.4
17. SMF Gallery Pro 1.4.5
18. PortaMx v0.957 0.957
19. SMF Gallery Pro SSI 2.0
20. Member Color Link 3.0.6
21. SMF Canonical Tag 1.2
22. SMF Gallery Pro Recent Comments Board Index 2.0
23. SSI Latest Members 1.0.1
24. MCLegendII RC1 3.0