This appears to be a bug in eCart when selecting to use PayPal Standard. I have logged this in the bug base.
To work around the issue, you will need to obtain API Credentials from paypal for use with Express Checkout.
Once you have obtained the api credentials, open the cehckout page and double click the "Authentication For PayPal Express Checkout" server behavior.
change the System to US and paste the API Username, password and signature into the appropriate places.
You will also need to edit the "Get Payer Profile For Paypal Express Checkout" and the "Process transaction with PayPal express Checkout" behaviors on the pp_confirm page.