User is trying to delete an expense entry, but receives an error message that the expense entry cannot be deleted as it is linked to a credit card transaction.
You cannot delete expense entries linked to credit card transactions. You need to first unlink the expense entry from that transaction. That can be done by clearing the Credit Card column of the expense entry in the Expense Entries screen (click More > Show/Hide Columns > Credit Card to make this column visible). When unlinked, you can delete the expense entry.
This can also be done from the Credit Cards screen, but you have to first identify the credit card transaction to which the expense entry is linked. After you have identified the transaction in the list view, click on it to open its details. Under the Items tab, delete the row of the expense entry in question. Core then automatically deletes the expense entry.
Alternately, if there are no other items linked to the credit card transaction, you can also directly delete it in the Credit Cards screen. Core then prompts you to delete the associated entries.