hey vladimir,
this problem is caused by some leftover folders from older versions. you can delete these folders like /administrator/components/com_easysocial/updates/1.2.1/ and this should fix it as mark suggested in this topic (with the exact same issue): http://stackideas.com/forums/in-es-dashboard-v1-2-6-clicked-on-maintenance-and-got-this-error-message-fatal-error-cannot-redeclare-class-socialmaintenancescriptfixalbumphotouserid-in

hope that helps and have a nice day