Question: We're on civicrm 4.7.5 on Drupal 7.

All contributions paid through the paypal standard payment processor are failing to successfully complete.

The user sees a successful transaction, but the contribution status is " Pending (Incomplete Transaction)"

There is nothing in the CiviCRM log to suggest an error. The IPN is sent to the correct URL, the status recorded in paypal is HTTP 200 OK.

But when I copy the path into a browser:

<https://[ourwebsiteurlredacted.com]/sites/all/modules/civicrm/extern/ipn.php?reset=1&contactID=9994&contributionID=5669&module=contribute&membershipID=9587>

this prints the following message to screen:

```
Sorry, can not load CMS user account.

```

Any help debugging would be greatfully received!

Answer: 
I think there is a bug here of some sort - I have reverted to an old copy of ipn.php, from 4.7.3, and payments are now completing successfully again
This is a really common error incidentally.

I suspect that that error you're seeing is unrelated to the PayPal issue.

1. Check the CiviCRM Error Logs for errors that happened around the time of the last transaction.
2. Check your htaccess logs for blocked requests from PayPal.
3. The error being thrown is in libraries/civicrm/CRM/Utils/System/Drupal.php line 545 in function loadBootStrap. This code is messy, with a function that does many things.
4. I would check visiting the IPN with the correct parameters in a browser and seeing if that updates the transactions as you'd expect.