Fix an error in my magento & make cron works

hi, I'm looking for someone experienced in Magento. 2 tasks to perform: 1 - I'm having from time to time an issue appearing on my site under magento linked w/ duplicate ID in the database (copy/paste below). 2 - Making CRON works (not sure if it has to be done on the admin or on the dedicated server iteself. I don't know the path for [login to view URL] on the server & the freelancer needs to know linux & SSH as well. I've a admin access where to create the CRON but never succeeded to find the right path to make it work). Seeing past similar request, this should'nt request more than 30$. COPY / PASTE of the issue described above: There has been an error processing your request Item (Mage_Catalog_Model_Product) with the same id "4971" already exist Trace: #0 /home/paraphar/www/app/code/core/Mage/Eav/Model/Entity/Collection/[login to view URL](265): Varien_Data_Collection->addItem(Object(Mage_Catalog_Model_Product)) #1 /home/paraphar/www/app/code/core/Mage/Eav/Model/Entity/Collection/[login to view URL](1057): Mage_Eav_Model_Entity_Collection_Abstract->addItem(Object(Mage_Catalog_Model_Product)) #2 /home/paraphar/www/app/code/core/Mage/Eav/Model/Entity/Collection/[login to view URL](871): Mage_Eav_Model_Entity_Collection_Abstract->_loadEntities(false, false) ...........