It's hard for us to give you a specific answer because PayPal only reveals so much information to us, but generally this happens if you try to pay with a method via PayPal that doesn't send the money immediately. For example if you needed to initiate a bank transfer before the funds get sent. Do you know what method you used within PayPal to send the funds?
PayPal is reported that the transactions is pending for the reason "OTHER." You can also try contacting their support about the transaction.
Sorry, hope that helps.
Thanks