I copied your directory set up, along with the filename, and ran your script on perl-5.12.0 on Windows 7 and it worked fine for me. I did add a couple of lines to check that both the file ($source) and the destination directory ($target) existed:

use strict;
use warnings;
use File::Copy;

my $source="C:\\sandboxes\\source_backup\\source_backup\\source_develo
+p\\source_folder\\source_part\\source_specific\\source_common\\rb_src
+c_sourcedevelopfolderpartspe_Interfacessourcecommonspecific.h";
my $target="C:\\sandboxes\\target_backup\\target_backup\\target_develo
+p\\generated\\_hnv_scan\\_source_develop\\source_folder\\source_part\
+\source_specific\\source_common";

print "OK 1\n" if -e $source;
print "OK 2\n" if -d $target;
copy($source,$target) or die "could not do: $!";
print ("done");
[download]

I got:

C:\_32\pscrpt>perl try.pl
OK 1
OK 2
done
C:\_32\pscrpt>
[download]

However, the first time I ran it, it failed because I had not named the $target directories correctly.
I had missed the underscores at the beginning of "_hnv_scan" and "_source_develop", and the script therefore produced:

C:\_32\pscrpt>perl try.pl
OK 1
could not do:  at try.pl line 10.
[download]

Please do check that both the $target directory and $source file do actually exist, as it seems to me that the most likely explanation of your issue is a typographical error.

Cheers,
Rob