Customers getting redirected to PayPal login

Hello,
I am having an issue with Paypal Express. I have had a number of customers call my actual store saying that they've tried to place an order, but it won't work.
I have tested the flow of the site and the issue seems to arise at the VERY last page of Paypal. When the user clicks "Pay Now", they just get redirected back to the first page of Paypal (the login page), and the order is not processed.
What gives? I have NO idea what is going wrong here. The more frustrating thing is that sometimes it will work. I tried 4 times to get it to work and only once did my test order go through. Any ideas?
I have also recently changed hosts. I am not sure if this will make any difference or not. I was having the same problem over the holidays, and contacted the new host. They were good enough to go through and place an order...and it went through. But now I'm having troubles again.

Thanks for your time,

Adrian

Is there anyone who is having this issue? Or are you using a checkout that you are happy with, other than Express?

Update: I have tried solving this problem by uninstalling the Paypal Express Mod from Zen Cart and creating new API information on my Paypal account and reinstalling the mod with this new info, but still the problem persists.
Any ideas...anyone?

Beama:

I have tested the flow of the site and the issue seems to arise at the VERY last page of Paypal. When the user clicks "Pay Now", they just get redirected back to the first page of Paypal (the login page), and the order is not processed.
I'm having trouble envisioning what you're describing.
Can you please explain in fine detail all the steps you're taking after adding a product to your cart?
Also, what currencies are you using? Tax configurations? Coupons/discounts?
Also, have you enabled debug-logging in the module? If not, turn it on (log-to-file) and zip-and-post the log files for review. (You can PM me the link to the zipped logs if you don't want them viewed publicly.) http://www.zen-cart.com/forum/showthread.php?t=61199

Hello Dr. Byte,
Thank you SO much for replying. These are the steps taken when I have the problems:

1. Product is added to cart
2. Customer has option to click either "checkout" or "checkout with Paypal"; cusomter clicks "checkout"
3. Customer is then shown a (moded) "Your Order Total" page that has all steps; Delivery Infomation & Payment Information on it. Here they can change Shipping or Billing Info and select there shipping option. They can choose to add special instruction and then they click "Confirm The Order"
4. They are shown "Your Order is being processed"; then forwarded to Paypals site. They are shown "Don't have a PayPal account? No problem, continue checkout." or "Log in to Paypal"; customer logs in or chooses that they don't have an account.
5. Either they fill in info then go to "Review Your Payment" page, or they are sent directly there if they have an account.
6. They click "Pay Now" and then they are returned to page: "Don't have a PayPal account? No problem, continue checkout." or "Log in to Paypal"; and no transaction has taken place. It's looping them back to the beginning.

*This happens MOST of the time, but not all the time.

I have left the currency to "Selected Currency"; I have the regular setup of taxes (followed directly from the tutorial); and I do not offer coupons or discounts.

I have run the log files, and I will PM you about them.

Thanks for ALL the help,

Adrian

Beama:

3. Customer is then shown a (moded) "Your Order Total" page that has all steps; Delivery Infomation & Payment Information on it. Here they can change Shipping or Billing Info and select there shipping option.
   I'm not intimately acquainted with the inner workings of the various addons which might accomplish the one-page layout you're describing. Thus I can only guess that the problems are related to the addon/modifications you've done to your checkout process.

It seems very odd that PayPal would return the customer back to the PayPal login page. It's not clear from your summary whether they URL takes the customer back to your store, which then sends them back to PayPal again.
But, again, with your non-standard checkout flow, there's little I can do to help.

Thanks for the help Dr. Byte. I have since shut off the Mod: Fast and Easy Checkout, and paypal is now working!
I guess there must be issues with using that mod and Paypal Express.

Thanks again.

Thanks for confirming :)