My old/somewhat recent minecraft world's can't be deleted or played on. When trying to join them it says "Failed to Sync World Data. Could not sync your world data. Would you like to try again?" After trying again I still can't join them. The world icon's are gray/white pictures of a classic minecraft world. When tried to edit these worlds it once again says "Failed to Sync World Data. Could not sync your world data. Would you like to try again?" 

These problems only happen on a world with a grayed out icon. All other worlds are working fine.