I recall a memorized transaction but get the "quantity falls below zero" again and again
Let me help you resolve this, Gerdgoebel.
We'll have to ensure the item's quantity is not zero or negative. It may be the reason why you encounter the message. Here's how:
Go to Item List.
Select an item, right-click, then choose Edit Item.
Check the quantity under On Hand.
If it's not zero quantity, though, this unexpected behavior can be caused by a corrupted file. Let's run the Verify/Rebuild utility to detect the data damage. Here's how:
Go to Utilities, then choose Verify Data.
If QuickBooks detected no problems, there's no further action needed. If you receive a message, "Your data has lost integrity," the file is damaged. Just continue to Rebuild Data to correct the problem.
When you Rebuild Data, you'll receive a message to back up your company file, just click OK. The utility starts as soon as the backup is finished.
Click OK when you get the message "Rebuild has completed."
Run Verify Data again to check for remaining data damage.
However, if it still shows zero, you can use the File Doctor tool to fix company file issues.
You can keep us updated after trying the steps. Get back to this thread if you need more help. Keep safe!