I am trying to install a Firebird server on a reasonably clean Windows
10 machine, but I am running into the gsec "cannot attach to password
database" issue.

Details are:

Edition: Windows 10 Pro (64-bit system, x64 based processor)
Firebird: SuperServer - both 32-bit and 64-bit versions attempted

Full error message (64-bit version) when running gsec from a command
prompt with administrator privileges:

C:\Program Files\Firebird\Firebird_2_5\bin>gsec -user sysdba -password
masterkey
use gsec -? to get help
cannot attach to password database
unable to open database

Also tried gsec with
-database "c:\Program Files\Firebird\Firebird_2_5\security2.fdb"
and
-database "localhost:c:\Program Files\Firebird\Firebird_2_5\security2.fdb"
and
-database localhost:"c:\Program Files\Firebird\Firebird_2_5\security2.fdb"

Server running as a service (tried both 32-bit and 64-bit - uninstalling
and rebooting in between)

Service appears to be running correctly.

Control panel applet is not installed.

FIREBIRD environment variable not set, no Firebirds in either system or
user PATH environment variables.

I have tried everything I could find on Google without joy, so thank you
in advance for any help with this!