Hi,
If you get the error "At this time, we are unable to process your request. Please return to xxx and try another option.", it's normal that the payment is cancelled... The payment didn't went through...PayPal said that they can't transfer the money, so if course the payment was not made, and the order was cancelled.
Normally, with that error you have another message which gives more details on why PayPal cannot process the request, if not you should contact the PayPal support and ask them why you have that error.
Also, make sure that if you use a normal account, you don't use the sandbox URL of PayPal in the plugin's options.