Applies to Magento 1.4 installations
For Magento 1.5 version and above please check this article
Symptoms
The following error (or similar) is shown in Magento Connect Manager on installation/upgrade:
ERROR: unable to unpack downloader/pearlib/download/AW_Blog-1.0.21.tgz
Cause
There is a bug in current stable PEAR/Archive_Tar implementation resulting in impossibility to unpack archives made by certain software versions.
Solution
To fix it simply replace downloader/pearlib/php/Archive/Tar.php file with a patched version or apply a patch from http://pear.php.net/bugs/bug.php?id=17578&edit=11.
The patch has been already applied for our new installations. If you notice this issue with your old Magento installation, please notify our Support Team to get this fixed.