cannot welcome message: warning: Attempt to assign property of non-object

Thank you for looking into it.

I experienced the bug on the live site and I could reproduce locally, after enabling rules and privatemsg for the first time. I don't see the 'receive private message' permission, but authenticated users have the 'read private message' and 'write private message' permissions. Same problem.

I *had* used the pre-configured role. On one site I edited it and when I enabled and saved it, I noticed the machine name was conveniently altered. On the other site, I used the 'clone' button and beside enabling it, I didn't do any specific change.

Here is the exported rule:

array (
  'rules' => 
  array (
    'rules_emsg_welcome_message_cloned' => 
    array (
      '#type' => 'rule',
      '#set' => 'event_user_insert',
      '#label' => '(clone) Send welcome message with privatemsg when a new user is created',
      '#active' => 1,
      '#weight' => '0',
      '#status' => 'custom',
      '#conditions' => 
      array (
      ),
      '#actions' => 
      array (
        1 => 
        array (
          '#type' => 'action',
          '#settings' => 
          array (
            'username' => '',
            'userid' => '1',
            '#argument map' => 
            array (
              'user_loaded' => 'admin_user',
            ),
          ),
          '#name' => 'rules_action_load_user',
          '#info' => 
          array (
            'label' => 'Load a user account',
            'new variables' => 
            array (
              'admin_user' => 
              array (
                'label' => 'Admin User (uid 1)',
                'label callback' => false,
                'type' => 'user',
              ),
            ),
            'module' => 'User',
          ),
          '#weight' => -10,
        ),
        0 => 
        array (
          '#info' => 
          array (
            'label' => 'Send a message',
            'arguments' => 
            array (
              'subject' => 
              array (
                'type' => 'string',
                'label' => 'Subject',
              ),
              'body' => 
              array (
                'type' => 'string',
                'label' => 'Body text',
              ),
              'recipient' => 
              array (
                'type' => 'user',
                'label' => 'Recipient',
              ),
            ),
            'module' => 'Privatemsg',
          ),
          '#name' => 'privatemsg_rules_new',
          '#settings' => 
          array (
            'subject' => 'Welcome!',
            'body' => 'Hey < ?php $account->name; ? >, welcome on our site!',
            '#argument map' => 
            array (
              'recipient' => 'account',
              'author' => 'admin_user',
            ),
            '#eval input' => 
            array (
              'rules_input_evaluator_php' => 
              array (
                'body' => 
                array (
                  0 => 'account',
                ),
              ),
            ),
          ),
          '#type' => 'action',
          '#weight' => 0,
        ),
      ),
      '#version' => 6003,
      '#categories' => 
      array (
      ),
    ),
  ),
)

On the local / test site, I got even more errors than I had when I first tested on the live site:

    Notice: Trying to get property of non-object in privatemsg_rules_new() (line 386 of privatemsg_rules.rules.inc).
    Notice: Trying to get property of non-object in privatemsg_user_access() (line 271 of privatemsg.module).
    Notice: Trying to get property of non-object in privatemsg_user_access() (line 271 of privatemsg.module).
    Warning: Attempt to assign property of non-object in privatemsg_recipient_format() (line 2782 of privatemsg.module).
    Notice: Trying to get property of non-object in privatemsg_recipient_format() (line 2783 of privatemsg.module).
    Warning: Attempt to assign property of non-object in privatemsg_recipient_format() (line 2783 of privatemsg.module).
    Notice: Trying to get property of non-object in privatemsg_recipient_format() (line 2785 of privatemsg.module).

I tried to debug the first of those error and inserted some calls to dpm() at the start of the first function:

function privatemsg_rules_new($subject, $body, $recipient, $author) {
dpm($recipient, "recipient");
dpm($author, "author");
  rules_log(t('Writing new message with subject %subject to %user from %author', array('%subject' => $subject, '%user' => $recipient->name, '%author' => $author->name)));

Both $recipient and $author are expected to be objects, Unexpectedly, it's not the $recipient that caused problems (at least at this stage) but the $author (i.e. user/1) who is not an object representing a user but an array representing the message:

author =>
   ... (Array, 4 elements)
        subject (String, 8 characters ) Welcome!
        body (String, 26 characters ) Hey , welcome on our site!
        #argument map (Array, 2 elements)
        #eval input (Array, 1 element)
            rules_input_evaluator_php (Array, 1 element) 

At this stage, I got stuck because I didn't manage to figure out who was the calling function.

That's all I've got.

P.S.
Above, I inserted some spaces in the PHP tags, because they were messing with the formatting of the comment within this issue.

'body' => 'Hey < ?php $account->name; ? >, welcome on our site!'

@Berdir: have you been able to reproduce with the requested info that I provided?