"You do not have sufficient stock to create out-transactions..."

"You do not have sufficient stock to create out-transactions..."

Hello, I received this error, trying to convert SO to invoice: 
"You do not have sufficient stock to create out-transactions for the item CMP 6. Please restock the item and try again."

But I DO have stock... Noticed that if this Composite item is bundled - there is no error. What could be the reason?

I also noticed that customer created via quick create (while issuing a SO) can't be found in a dropdown field when creating a Sales Order.

Thanks