If you receive the error message: Business Validation Error: There is no account associated with the item. Is it marked for purchase, and has an account associated with it?
First make sure that the item exists in your products and services list. If you are using sub items be sure that your import file includes both the Item and the sub item separated by a colon.
If the item does exist in QuickBooks Online then go edit the item in QuickBooks Online and make that you have selected the box next to: I track quantity on hand.... and have provided an Expense Account.
See screen shot below.