我无法在wordpress 3.0中安装任何主题/插件

Downloading install package from http://downloads.wordpress.org/plugin/contact-form-7.2.3.1.zip…    
Unpacking the package…    
Installing the plugin…    
Could not copy file. /public_html/blog/wp-content/plugins/contact-form-7/languages/wpcf7-lt_LT.po    
Plugin install failed.


Downloading install package from http://wordpress.org/extend/themes/download/piano-black.2.2.zip…
Unpacking the package…
Could not create directory. /public_html

Downloading install package from http://downloads.wordpress.org/plugin/contact-form-7.2.3.1.zip…
Unpacking the package…
Could not create directory. /public_html/blog/wp-content/upgrade/contact-form-7.tmp/contact-form-7

Update 12/01/2012: 如果您使用的是最新版本的WP（3.1及以上版本，从今天起为3.3.1），则不会有任何问题。这些问题已被删除。享受你的WP。