Hi - I have another site that's started getting this generic error message, seemingly from nowhere without any changes to my site. I've read through all the other similarly-titled posts and none of those seem to have a solution that has worked for me.
The specific problem is this; if I add an item to my shopping cart, the first one goes in fine. If I then hit 'continue shopping' and add a second item (the same item again or a different one, it doesn't seem to matter) then I end up on the error page. However, if I wait for a while (10-15 minutes I guess, I haven't been able to time it accurately) then I can successfully add a second item to the cart. When I get the error, the page goes through the URL "https://www.paypal.com/auth/validatecaptcha" first for a few seconds before landing in "https://www.paypal.com/webapps/shoppingcart?mfid=1516216653381_61cba1fc93d29&flowlogging_id=61cba1fc...".
I've used Chrome's DevTools to check the form data from the button - it all looks to be OK, no stray currency symbols or extraneous spaces that I can see, and as I mentioned this is code that's been working fine for years before going down over the last weekend.
My website is http://www.brigademodels.co.uk; if anyone is good enough to want to try it out, you'll need to select a shipping destination first on this page before the 'view cart' and 'add to cart' buttons are enabled :http://www.brigademodels.co.uk/Shopping/select.html