Hi

> AFAIR, connected user (not firebird user but windows user) has to have

file permissions on security.fdb. I.e. if you connecting from client
computer where user1 is logged in, user1 on server should be able to read
and write databases files.

> Try to put security.fdb and database to FAT where ACLs aren't supported.

NO
The Firebird server known nothing about the OS user of the firebird client.
security.fdb need to be accessabe by the Firebird Server user only. This
means the user, the server is running as. For services this is usually
SYSTEM.

Regards,
Steffen