Skrill sees PayPal as a competitor and makes it difficult for the customers to tie Skrill cards to PayPal wallets. When you try adding a Skrill prepaid card to your PayPal wallet, the confirmation transaction never shows up on Skrill to get the PayPals confirmation code.
SOLUTION
In Paypal - add the card to the wallet, request a confirmation transaction to verify the card.
In Skrill - go to MY CASES and create a case, requesting the info on your hidden PayPal transaction, wait for the answer with the payment info and the PayPal verification code.