Problem:
Getting error "Operating System Directive Open failed -- Permission 
denied" when trying to connect in Interbase 4.0.

Solution:
Check the followings:

*  The user has sufficient permission to the lock file.  The lock 
file usually looks something like "isc_lock1.pooka".  If not, remove 
old lock file and recreate lock file by connecting to a database as 
root.  Or change the permission on the lock file to 666 mask. 

*  Make sure the IB server has the valid IB server license.