>If I'm not mistaken, I think you just need to remove the "string" from your call to GetItemsByCategor()......

I think the whole code was wrong, as I just found out. All I think I need was

/// <summary>
        /// Get Inventory Dictionary for passed category
        /// </summary>
        /// <param name="Category">Category</param>
        /// <returns></returns>
        public Dictionary<string, string> GetInventoryDictionaryByCategory(string Category)
        {
            Dictionary<string, string> list = new Dictionary<string, string>();            

            InventoryDS.ItemsDataTable dt = this.GetItemsByCategory(Category);                

                foreach (InventoryDS.ItemsRow dr in dt.Rows)
                {
                    list.Add(dr.itemdesc1, dr.pk.ToString());
                }                            

            return list;
        }

But let me re-test.