> The client is currently using Firebird version 1.52.

Superserver or classic?

> In the most recent occurence, the first sign of something wrong according to the log file was this:
>
> FS2 (Server) Tue Jul 21 00:19:47 2009
> Database: D:\LABORPOWER\DATA\LPIBEW25.GDB
> I/O error for file "D:\LABORPOWER\DATA\LPIBEW25.GDB"
> Error while trying to read from file
> The process cannot access the file because another process has locked a
> portion of the file.
> internal gds software consistency check (error during savepoint backout
> (290))

I would recommend to change DB file extension ASAP.

> 1) We recently found out that the client was doing a nightly tape backup which includes the .gdb database file.
> Could this be causing any the problems?

Yes, backup process do exactly what is written above - lock portion
of file. The same can do an anti-virus.

SY, SD.