PHP Fatal error: Only variables can be passed by reference in /var/app/current/sites/all/modules/ctools/includes/uuid.inc on line 28

You've logged this against -dev, so I can't tell what line 28 refers to; but in my version it would be this:

24 /**
25  * Generates an universally unique identifier using the PECL extension.
26  */
27 function _ctools_uuid_generate_pecl() {
28   return uuid_create(UUID_TYPE_DEFAULT);
29 }

which seems like it should be okay, if I'm understanding the source code at PECL correctly.

Can you confirm which code your error is referencing, and the version of the PECL uuid package you're running?

This error message is received by the user when hitting the 'upgrade and save' or the 'save' button on either a panels 'content' pane page or when saving a new block content piece for a panel.

I've also been able to replicate this issue using ElasticBeanstalk with a PHP version of 5.5.12 - interestingly, both with the dev version tagged here and with the recommended 7x release. I am, however, unable to replicate the issue locally using 5.5.10, 5.5.14, and 5.5.18. My working hypothesis is that there's something wonky going on with the PHP version for this particular ElasticBeanstalk environment - I'm currently in the process of setting up a new environment with a higher PHP version and will report back with my findings.

The complete error message received is:
An AJAX HTTP error occurred.
HTTP Result Code: 200
Debugging information follows.
Path: /panels/ajax/editor/add-pane/panel_context%3Apage-campuses_landing%3A%3Apage_campuses_landing_panel_context%3A%3A%3A%3A/right/custom/custom/form
StatusText: OK
ResponseText: Fatal error: Only variables can be passed by reference in /var/app/current/sites/all/modules/contrib/ctools/includes/uuid.inc on line 28

Upgrading did NOT resolve this issue. Please advise, ! Sylvain.

I'm having this same issue on AWS EB. Looking forward to an answer, if I find one i'll posit it here.

As per comment #2: Can you confirm which code your error is referencing, and the version of the PECL uuid package you're running?

In fact, this issue seems like a duplicate of these:

* ctools: #2354877: uuid_create function cause fatal error for php > 5.3
* uuid: #2349237: Fatal error: Only variables can be passed by reference in /var/www/html/drupal-7.29/sites/all/modules/uuid/uuid.inc on line 164

I suggest that you assist with those.

Just worked with the Dire. of IT at my job for a few hrs putting this issue to bed. Make sure php isn't loading your uuid module and apache isn't doing loading it either. As soon as we disabled it from loading the problem went away.

Sounds like this is a bug in CTools and not Panels.

Looks like it may have been fixed in ctools with #2354877: uuid_create function cause fatal error for php > 5.3