Not getting the IPN from Paypal on event registrations

[Upperholme]

I've sent up an event, am using Paypal standard and using the Paypal sandbox to test drive my event registration.  It looks like the IPNs are not being received. Paypal reports everything as fine, but contributions are recorded as pending and no emails are being sent.

Browsing to http://mysite.com/sites/default/modules/civicrm/extern/ipn.php I get the following:

"Could not find valid configuration dir, best guess: /srv/www/vhosts/mysite.com/httpdocs/sites/default/modules/civicrm/../../sites

If this is a standalone installation (i.e. not a Drupal or Joomla module) and you'd like to re-initialize it, click here."

Which suggests that something is amiss. Also I don't have a CiviCRM.log file in my /files/civicrm/upload/ directory.

Any pointers welcome.

[Upperholme]

Update. Looks like civicrm.config.php is not checking sites/default:

line 70:      if ( strpos( $currentDir, 'sites' . DIRECTORY_SEPARATOR . 'all' . DIRECTORY_SEPARATOR . 'modules' ) !== false ) {

I edited this to:

     if ( strpos( $currentDir, 'sites' . DIRECTORY_SEPARATOR . 'default' . DIRECTORY_SEPARATOR . 'modules' ) !== false ) {

and it all seems to be working fine now.
Of course I would normally install civicrm in sites/all/modules, but it just so happens that i inherited this install from someone else, who put all the modules in sites/default/modules, so I installed civic there as well.

Still no CiviCRM.log file though.

And it appears that my site is sending out two registration confirmation emails, about 1 minute apart?