what is giving the error sites/default/modules does not exist
Here are a few other possibilities than Xavier's, which seem on point but not yet solving issue:


Check the entries in Administer > System Settings > Directories to see if the sites/default/modules directory appears anywhere and adjust as appropriate if it does. 
Using phpMyAdmin or equivalent, check in the Drupal database in the registry table filename field for a module with a path at sites/default/modules. If you find one, change it to sites/all/modules after ensuring it is there.