As of some days back, PayPal has changed, without any prior notice, the way they process the "Add to Cart" buttons code.
Specifically, in the Add to Cart code, you can include a field named "image_url". The value of this field is the URL of your Cart Header Image. So if you wanted to "show" PayPal where to get this image (Logo) from, you could include the URL as value of this field. This line of code looked like this:
<input type="hidden" name="image_url" value="">
BlueVoda PayPal Button Generator never made use of this field. However, it included it in the code, with NULL value.
This was ok up to some days ago. PayPal would process the code ignoring this field since it's value was null.
This in not true any more. PayPal will display an Error Message saying "Some required information is missing or incomplete. Please correct your entries and try again."
The only way to avoid this, is to change the Add to Cart button code.
The BlueVoda Team is preparing a BV update that will solve the problem. You only need to open your pages in BV and then publish them again. It is advisable that you check the settings to make sure they are correct.
Until this update is ready, a solution could be to re-create the buttons in PayPal's site and replace the BlueVoda Add to Cart buttons, with html boxes where you will paste the code created in PayPal.
Another simple solution: whilst you are in BV, right click the Add to Cart image. Select HTML, and view the code. Copy it, and paste it in the html box. Delete the ENTIRE "image_url" line. Save and publish.
The estimated time for the BV update is 24 - 48 hrs.