How to install Drupal 7 on Ubuntu?
This could be a bug, see:


https://bugs.launchpad.net/ubuntu/+source/php5/+bug/1315888
https://bugs.php.net/bug.php?id=53829


As I had the same error and after deep diving I reached to modules/system/system.tar.inc at line 716 which calls gzopen(). Here the errors are suppressed using @.

Actually its giving following error on ubuntu 14.04:

Fatal error: Call to undefined function gzopen() in /var/www/html/drupcom/modules/system/system.tar.inc on line 718


So this is issue with Zlib. 
I've tried to solve it using 
these instructions, but no luck. Then I found that it is known bug.