kolab roundcube plugins vs. roundcube 0.8.5 calendar plugin problem

[Janos SUTO]

Hello,

I tried to install your calendar plugin for roundcube 0.8.5. I copied 
the calendar
directory to roundcube/plugins, added 'calender' to roundcube's plugin 
list.
I created the required sql tables: mysql <  
drivers/database/SQL/mysql.initial.sql

Now when I visit the roundcube installation, I got a white empty screen 
only.

What am I doing wrong?

Best regards,
Janos