Help!!! I Can't Buy Lindens, What Can I Do??

I'm quite new here. I have a problem. I can't buy lindens in second life. I'm a verified Pay Pal member. Everytime I tried to buy lindens it says :

We are unable to complete your request:
Could not charge account.
The system encountered an error while processing your order, please try again.


It's very weird because I can buy products in the web pages buy them by paypal but ONLY paymments in dollars. Can you Help Me with this problem?? because it's very unconfortable to buy things by web and one by one. What can I do??

Thank you!!

Have you provided payment information on your account page here yet?:

https://secure-web10.secondlife.com/my/account/billing.php?lang=en-US

The web shopping and in-world money systems are separate, because at one time SXtreetSL was a separate business that Linden Lab bought.