public IList<Website> Get()
{
    //The `_cacheManager.Get` just retrieves the object from an `ObjectCache` instance based on key.
    return _cacheManager.Get(CcCacheWebsiteAll, () => _websiteRepository.Table.ToList());
}

var store = new Store();
store.Name = "something";
store.Website = _websiteService.Get().FirstOrDefault();
_storeService.Insert(store);

//Where _storeService.Insert(store) is:

public void InsertStore(Store store)
{
    _storeRepository.Insert(store); //THIS will raise the error
}