Paypal transactions not completing.

[RodG]

I downloaded a copy of the source and did a file comparison of every paypal file in the in the /includes/modules/payment.... directory and subdirectories and the ipn_main_handler.php files. They were exactly the same, so the problem has not been caused by a difference in the files.

Sweet. Knowing this narrows things down a lot.

The weirdest thing is that some of the transactions complete successfully. I could accept that there was something wrong with the implementation if it failed 100% of the time... but it doesnt.

This now points back to one thing.. It's not the ZenCart code that is causing the problem, it is something server related.

Until/Unless demonstrated otherwise this is my 'final' diagnosis. I can't imagine what else it could be.

Possible causes :
Server overload
Server software being updated or patched (bad timing)
?????

Cheers
RodG

[DrByte]

Its running PalPal Express checkout rev1.5.4

You said you're using Express Checkout, but the only logs you're posting are from IPNs.
Transactions originating as Express Checkout transactions do not get added to your store via the IPN process. In Express Checkout mode, he IPN process is simply a notification tool to update the status of transactions.

So, if your store doesn't have the transactions stored properly, then the rest of the checkout code that happens immediately after PayPal receives the "complete this transaction" instruction, is failing. Presumably because that part of the code on your server is altered in some way.

While comparing all the paypal files against originals is useful, it doesn't tell us anything about the ways in which your store has been altered from original code and original function. And yet therein likely lies the answer to your unique problems.