# Hash, this is what you have
my %hoh = ( ... );
# walk each key/value pair contained in the hash reference stored in $hoh{$sid}
while ( my ( $key, $value ) = each %{ $hoh{$sid} } ) { 
...
}

# Hash reference, what generated the error
my $hoh = { ... };
# walk each key/value pair contained in the hash reference stored in $hoh->{$sid}
while ( my ( $key, $value ) = each %{ $hoh->{$sid} } ) { 
...
}