"10408 Express Checkout token is missing" error message

I am using Zen-Cart v1.3.8.

I recently installed (or tried to install) 2CheckOut to run in conjunction with PayPal Express Checkout. (I began installing 2CO but got hung up with some fine-tuning and put it on hold for a day - disabled it but left the module installed.) In the meantime, it messed up the PayPal orders and customers were unable to order from PayPal. Concerned about losing customers, I uninstalled the 2CO module and removed all 2CO files from the server until I could get back to looking at it in more detail.

PayPal Express Checkout orders are coming through again now, but I received one message (and one message only, even though I received more than one order) that said "10408 Express Checkout token is missing". The order still went through fine, and the funds were deposited into my account.

Is this something I have to worry about? Was it a one-time thing?

If it's relevant, the order I received the error message for was the first order I got after uninstalling the 2CO module - the following orders did not give me error messages. This causes me to think maybe it was just a fluke, and has nothing to do with 2CO.

Sorry for the wordiness - I just think the more information you have, the easier you can diagnose the problem. Thank you in advance for your reply.. much appreciated.

Unless the 2CO module touches any existing files, it shouldn't have any impact on PayPal payments. That said, 2CO has always been a flakey service in my experience. That said, many still use it.

As for your "10408 Express Checkout token is missing" message, that should only occur if someone has tampered with the original Zen Cart code that handles PayPal payments. My first inclination is to compare all the files on your server against the original Zen Cart file zip archive to see if any unexpected changes have been made, either by rogue activity or (more likely) by bad uploads or bad edits on patching/editing files.
If it's only occurred once, it truly could be a fluke and might be easily blamed on a quirk in communication between your server and PayPal's server that was short-lived.