gbak backup error - Doesn't always stop at the same place. Would
stopping the server and doing a backup with no users, then a restore
help? So far has happened during daily gbak runs.

Do I need more memory for lock manager? (firebird.conf)

What's the next stable release I should migrate to?

I replicate two servers like this to each other. How will this affect
licensing, replication implementation if I migrate?

Server is...
Classic fb 1.5.3 on RHEL3 linux
FirebirdCS-1.5.3.4870.i686.rpm

command used...
/opt/firebird/bin/gbak -B -V -USER SYSDBA -PAS xxxxxxxxx
/data/fb/mydb1.fdb /data/fbk/mydbB1.fbk 1536m /data/fbk/mydbB2.fbk 1536m
/data/fbk/mydbB3.fbk 1536m /data/fbk/mydbB4.fbk 1536m
/data/fbk/mydbB5.fbk 1536m /data/fbk/mydbB6.fbk

from error log...
. . .
gbak: 26160000 records written
gbak: 26180000 records written
gbak: 26200000 records written
Fatal lock manager error: invalid lock id (3895040), errno: 2
--No such file or directory
Sat Nov 1 03:21:48 CST 2008