PayPal - "This transaction is invalid"

[winterstorm]

Hi, just setting up payment mods for my zen-cart 1.3.7.1, but neither the Pay Pal IPN nor Xpress Checkout seem to work. Both methods return the same error:

"This transaction is invalid. Please return to the recipient's website to complete your transaction using their regular checkout flow."

Has anybody experienced this before?

Any help is greatly appreciated...

Cheers,
WS

[DrByte]

What currencies have you configured?
Are you using coupons in your store?
What's the site URL?
What addons/contributions have you installed?
Please turn on PayPal debug log-to-file, do some test transactions, download the log files, zip them, upload the zip to your server, and post a link to the zip so the files can be reviewed.