Do anyone have any idea about this error ?

user@user-System-Product-Name:/etc/init.d$ sudo openerp-server start
Traceback (most recent call last):
File "/usr/local/bin/openerp-server", line 5, in <module>
pkg_resources.run_script('openerp==7.0', 'openerp-server')
File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 499, in run_script
self.require(requires)[0].run_script(script_name, ns)
File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 1235, in run_script
execfile(script_filename, namespace, namespace)
File "/usr/local/lib/python2.7/dist-packages/openerp-7.0-py2.7.egg/EGG-INFO/scripts/openerp-server", line 5, in <module>
openerp.cli.main()
File "/usr/local/lib/python2.7/dist-packages/openerp-7.0-py2.7.egg/openerp/cli/__init__.py", line 51, in main
__import__(m)
File "/usr/local/lib/python2.7/dist-packages/openerp-7.0-py2.7.egg/openerp/modules/module.py", line 82, in load_module
mod = imp.load_module('openerp.addons.' + module_part, f, path, descr)
File "/opt/openerp/server/openerp/addons/document_ftp/__init__.py", line 22, in <module>
import ftpserver
File "/opt/openerp/server/openerp/addons/document_ftp/ftpserver/__init__.py", line 26, in <module>
import abstracted_fs
File "/opt/openerp/server/openerp/addons/document_ftp/ftpserver/abstracted_fs.py", line 16, in <module>
from document.document import get_node_context
ImportError: No module named document.document

Somebody please help me to resolve it