I have updated from 8.5 to 9.1.1 and now when there is an item only to sell and a player wants to sell that item, they cannot sell it and it throws the player to the main menu of the store.

This occurs when the player right-clicks the item to sell.

This has been fixed in 9.1.2. Updating will fix this error when using Alt-Sell.

Thanks for the report!