"Your shopping cart is empty"

ah nvm. got this resolved by trying out the instructions here.
http://www.gravityhelp.com/forums/topic/wont-go-to-pay#post-45034

A Single Product Product Field that has "Disable Quantity" checked will require another Quantity Field (Hidden) with value set to 1 in order to work.

hmm strange. I am on 1.6.3 as well.. but the bug remains :/
I had to add the quantity fields before my form started working proper.

any ideas?
http://www.singaporemun.org/register

Hmm, potentially - I just did a quick test on my dev site with a single product with quantity field disabled and it went to PayPal just fine.

http://grab.by/c5vM and http://grab.by/c5vO

Does this first screen shot look similar to how you have your product setup?

I just made mine required and it went through fine again. If you want to send login credentials to your site you can use the support form:

http://www.gravityhelp.com/priority-support/

Just reference this post.

I had this same issue and just got things figured out. I had a couple sets of radio buttons which let my users choose one of 11 membership categories. Then I had 11 Single Product fields (one corresponding to one of the 11 membership categories). The Single Product fields each had the quantity field disabled. The Single Product fields also had conditional logic to show and hide them based on the values of the radio buttons.

I added the 11 hidden quantity fields with a quantity set to 1. Even with this, nothing got to PayPal.

What I finally figured out is that each of the 11 hidden quantity fields had to have the exact same conditional logic to show/hide them. The conditional logic had to match the conditional logic for the Single Product fields.

Once I did that all, everything works. It took a couple hours of work, but I got there.

Can you export your form and send the XML file to me to rob@rocketgenius.com