We have a 19 GB, single file database that is giving us the following
error when trying to restore from a backup (using gbak):

Fatal lock manager error: invalid lock id (<id>) errno: 2
--No such file or directory

When looking through the firebird.log file we are also finding the
following entry:

Fatal lock manager error: invalid lock id (<id>) errno: 0

System Specs:
~~~~~~~~~~~~~
Firebird - Classic v1.5.3
OS - RedHat Advanced Server 4 (kernel 2.6)
CPUs - Dual Intel 3.06 GHz hyper-threaded processors
Memory - 3GB
HDD - SCSI 75GB Raid 1 (15000 rpm)
File system - EXT3

The database is operational and we have not seen any user errors to
date but when trying to backup and restore in our weekly maintenance
window the restore fails whilst restoring privileges.

The database grows by about 2-3GB per month and is mostly used for
reporting purposes and it has at any time between 1-5 concurrent
connections. There are nightly Stored Procedures that are used to
summarise the detailed data into summary tables and it is only these
tables that have data deleted from them.

Please can someone shed some light on this for us