You forgot your closing </code> tag.

use strict; 
my $drive;
my $count = -1;
open( LIST, "tpconfig -l|" ) or die $!;
while( <LIST> ) # I added the <LIST>... which I suspect you had.
{
    ($drive) = unpack '@0 A8',$_;
    ++$count if m/^drive/;
    system("tpconfig -delete -drive -index ${count}");
    # You should check all system calls for error.
    # system will set $? to an error code for you.
}
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As for your errors... they don't look Perl related. Perhaps there is some other reason that you can't delete a drive... like some process has some kind of lock on a file in the drive.

Update: You can read up on $? here

Another Update: raj8 says the script deletes the drives, but still generates the errors.
The "problem" is that system doesn't capture STDERR. The way to circumvent this is to redirect to nul: BUT BEWARE! This will hide ALL error messages from the system call!
Try this:

system("tpconfig -delete -drive -index ${count} 2>nul:");
die "Unknown Error with tpconfig $count" if $? >> 8;
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Also, be sure to read chromatic's post. He raises a good point about when you make the system call, although I suspect that since there are only two robots and four errors that this isn't the complete answer. (Although I would bet good money that it does explain the duplicity of the index 0 error).