a (different) library question

[steve%prd.co.uk@localhost (Steve Blinkhorn)]

I have a small problem with a dynamically-linked library that I think
needs a better understanding than I have over how these are
discovered.

I have two essentially identical machines that are application servers
for our customers.  The custom software that provides the service is
32-bit, and has been running for years on i386 machines, and runs
perfectly on one of the new servers, and nearly perfectly on the
other.   But 'nearly' is not good enough.   An error is thrown at one
particular point, of the style "Sharedobject libxxxx.so not found".
Said shared object is in /usr/local/lib on both machines, and only in
/usr/local/lib.   Neither machine has any ld.so.conf file, nor is
there a library search path in the environment.   What is really odd
is that I can see where the error occurs, but I cannot imagine how the
program runs at all without being able to access the particular
library in question.   The two instances of the software have the same
file size and datestamp, as do the two instances of the library.

Is there some (to me) obscure detail or aspect of configuration of the
systems that I may be missing, or is there some way of discovering
what the effective search path is at the point where the error occurs?  
It happens in a Tcl script which is generating HTML from a database:
the failure does not crash the software, but happens every time a
particular component of the library is called, with the result that
the HTML ouput contains only the constant parts of the output, not the
variable data.   

-- 
Steve Blinkhorn <steve%prd.co.uk@localhost>