# See indexer.pl for a description of the data structures:
my %inv_index_db;
my %docs_db;
my %urls_db;
my %sizes_db;
my %desc_db;
my %content_db;
my %titles_db;
my %dates_db;
my %terms_db;

[line-77] tie %inv_index_db, $db_package, $INV_INDEX_DB_FILE, O_RDONLY
+, 0755 or die "Cannot open $INV_INDEX_DB_FILE: $!";   
tie %docs_db,      $db_package, $DOCS_DB_FILE, O_RDONLY, 0755 or die "
+Cannot open $DOCS_DB_FILE: $!";   
tie %urls_db,      $db_package, $URLS_DB_FILE, O_RDONLY, 0755 or die "
+Cannot open $URLS_DB_FILE: $!";   
tie %sizes_db,     $db_package, $SIZES_DB_FILE, O_RDONLY, 0755 or die 
+"Cannot open $SIZES_DB_FILE: $!";   
tie %desc_db,      $db_package, $DESC_DB_FILE, O_RDONLY, 0755 or die "
+Cannot open $DESC_DB_FILE: $!";   
tie %content_db,   $db_package, $CONTENT_DB_FILE, O_RDONLY, 0755 or di
+e "Cannot open $CONTENT_DB_FILE: $!"; 
tie %titles_db,    $db_package, $TITLES_DB_FILE, O_RDONLY, 0755    or 
+die "Cannot open $TITLES_DB_FILE: $!";   
tie %dates_db,     $db_package, $DATES_DB_FILE, O_RDONLY, 0755 or die 
+"Cannot open $DATES_DB_FILE: $!";   
tie %terms_db,     $db_package, $TERMS_DB_FILE, O_RDONLY, 0755 or die 
+"Cannot open $TERMS_DB_FILE: $!";   

my (@force, @not, @other);
my (@docs, @valid_docs);
[download]

From that code, it seems that $db_package is empty. This is most likely a configuration error. Ask your system administrator or the person who configured that script for you how to fix it.