为什么在运行“pear install phpunit / PHPUnit-3.7.35”时出现“ERROR:commit failed”?

Why do I get the following error while running "pear install phpunit/PHPUnit-3.7.5"?

pear install phpunit/PHPUnit-3.7.35

downloading PHPUnit-3.7.35.tgz ...
Starting to download PHPUnit-3.7.35.tgz (116,326 bytes)
.........done: 116,326 bytes
Could not delete C:\Zend\Zendserver\phpunit, cannot rename C:\Zend\ZendServer\.tmpphpunit
Error: commit failed

NOTE: I am running CMD in Admin mode in Windows 7 x64 and I specifically need this version (the latest 3.7 and not version 4). Also, I've tried setting permissions of that directory to be recursively not read-only, yet that doesn't work.