You can't delete list records that are in use on transactions.
To delete a name, first it must be removed from any transactions where it is in use.
Instead of deleting, you can merge customers into another customer:
First, rename one of your unwanted customers to something like "Consolidated Customers". Then go to the next unwanted customer and rename it to the same thing. QuickBooks will ask you if you want to merge the customers. Indicate Yes.
