Runtime error '94' invalid use of null

[gapsbottlestore]

I can scan the products I want to sell on the point of sale but every time I try to sell themF10 I get the following error, "Runtime error '94' invalid use of null". I double checked the cost and selling prices and it still does the same thing. I even downloaded the upgrade and installed it but it did not solve my problem.
After I created the stock items I put in the quantity by the "Adjust Stock Quantity Tab" under the stock take menu. was that the right way of doing it? Please help

[Admin]

As mentioned in my reply to your email :

You have sold some items on this specific transaction that contained a zero cost and / or selling at the time!

1. Open up 4POSScan & enter your password.
2. Press Ctrl-F8 to delete the transaction in the active POS window.
3. When prompted - specify YES to delete.
4. Re-ring up the items & continue.

[vip]

HI, tried the above fix and  does not help.

[Admin]

Is the Ctrl-F8 asking your to delete the transaction?

If not - check your keyboard layouts. Ctrl-F8 is the default for deleting the transaction.