Cart Gets Stuck on Step 2 of Checkout

My cart worked PERFECTLY last week and now nothing!

I had changed from the standard green template to Cold Steel (changed back) and that wasn't the issue.

When I'm going through the checkout process, I can get to PayPal, fill out the information and then hit their "submit" button. At which time, I'm returned to Step 2 of the checkout on my cart. The money is not coming out of my personal PayPal account nor is it going into my business PayPal account.

I'm not sure where to look for the error.

And I am using the most current version of Zen Cart.

EatStayPlay:

The money is not coming out of my personal PayPal account nor is it going into my business PayPal account.

Sorry but you can't use your own account to test paypal...
Has a customer emailed you on this problem yet????

Allow me to clarify: I have my business PayPal acct (info@) and my PERSONAL (kim@)

And as for customers, my cart is less than 2 weeks old. I think I had somebody TRY to buy something since my email inbox filled up with error log emails. Unfortunately, I have no idea WHERE in those emails I need to look to discover what is broken.

Look here first for any error log..
Report back any error here:

root directory/ cache

I just tested buying a product when I wasn't logged into the cart and it worked just fine. But when I'm logged in, the cart GOES to step 3, I complete PayPal processing and then I get returned to Step 2 in a never ending loop.

Help!