Due to a contractual agreement betweeen VMware and Veeam, Veeam Backup version 3.1 does not support VMware free ESXi. Veeam Backup 3.0 does support free ESXi 3.5. Customers who purchased Veeam Backup 3.1 prior to June 3, 2009 and are running VMware free ESXi 3.5 can contact Veeam support for a patch to allow backups. Customers who purchased Veeam Backup 3.1 after June 3, 2009 must use a paid version of VMware.