If you check the return status of backticks (qx) with $? you may get more information about your problem (Basic debugging checklist tip #7):

print $? if $?;
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Another quick thing to try is to replace the tilde with a full path:

`tar -xf $tarfile -C /home/foo/path_to_dir`;
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See also: What's wrong with using backticks in a void context?