erreur de configuration / bootstrapping de l'application

"/var/log/opendata/error.log" cannot be opened with mode "a"

#0 /opt/vdb/shared/ZFBesancon/VDB1Skeleton/library/VDB1Skeleton/Application/Bootstrap.php(118): Zend_Log_Writer_Stream->__construct()
#1 /opt/vdb/shared/zf1-future/library/Zend/Application/Bootstrap/BootstrapAbstract.php(673): VDB1Skeleton_Application_Bootstrap->_initLog()
#2 /opt/vdb/shared/zf1-future/library/Zend/Application/Bootstrap/BootstrapAbstract.php(626): Zend_Application_Bootstrap_BootstrapAbstract->_executeResource()
#3 /opt/vdb/shared/zf1-future/library/Zend/Application/Bootstrap/BootstrapAbstract.php(590): Zend_Application_Bootstrap_BootstrapAbstract->_bootstrap()
#4 /opt/vdb/shared/zf1-future/library/Zend/Application.php(389): Zend_Application_Bootstrap_BootstrapAbstract->bootstrap()
#5 /opt/vdb/www/opendata/data/trunk/code/public/index.php(56): Zend_Application->bootstrap()
#6 {main}