Extension package install error in Joomla 2.5 - Joomla! Forum - community, help and support

hi:
please me resolve extension install error!

new joomla. have experience other ecommerce content page builder (prestashop).
anyway, trying create simple cms page using joomla 2.5 , default template beez-20.

need create drop down sub-menu of top menu items. know beez-20 template doesn't support drop down menu. trying install dj-multitreemenu http://dj-extensions.com/dj-multitreemenu , dj-menu http://dj-extensions.com/dj-menu menu extension. downloaded package (.zip files joomla 2.5).

am getting error while attempting install package (from extension manager | upload package file | choose file (mod_djmultitreemenu_v1.6.4_j2.5.zip) | upload & install). error message below:

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jfolder::create: not create directory
module install: failed create directory: /srv/www/htdocs/joomla/modules/mod_djmultitreemenu

note that, install directories have been set "chmod 777" permission.

system information below:

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php built on    linux linux-z583 3.1.10-1.16-desktop #1 smp preempt wed jun 27 05:21:40 utc 2012 (d016078) i686
database version    5.5.25-log
database collation    utf8_general_ci
php version    5.3.8
web server    apache/2.2.21 (linux/suse)
webserver php interface    apache2handler
joomla! version    joomla! 2.5.6 stable [ ember ] 19-june-2012 14:00 gmt
joomla! platform version    joomla platform 11.4.0 stable [ brian kernighan ] 03-jan-2012 00:00 gmt
user agent    mozilla/5.0 (x11; linux i686) applewebkit/535.1 (khtml, gecko) chrome/14.0.835.202 safari/535.1