Not that I have an answer, but I would tackle this by placing debug statements in your cgi right before each execute. If you print, to stderr, the sql statement and the bind values, you can then inspect the apache (or whatever web server) error log for the actual sql that is causing problems. Once you've isolated the actual sql, check it out via isql or sqsh to see if it really is a problem on the database server end (the error statement makes me think the database server is having problems - but who knows, you could be sending it faulty sql).

On another note, check out the DBI and DBD documentation for a slightly better approach on executing sql. I prefer setting the RaiseError flag and then wrapping the actual executes in evals. That way the driver will not spill out error messages that will cause your webserver to barf - but you will have enough info to know what to do:

my $dbh = DBI->connect(
                  "dbi:Sybase:database=xxx", "user", "pass",
                  { RaiseError => 1 } );

eval {
      my $sth = $dbh->prepare( $sql );
      $sth->execute();
       ...
};

if( $@ ) {
    print STDERR "An error occurred: $@\n";
} else {
    print "All is right\n";
}
[download]

-derby