Front end Fatal error in sandbox mode

After:
* getting my install moved to the right PHP version at WPEngine,
* installing this plugin this morning May 5, 2016
* sucessfully tested a sale.

Now however, on my root home page I get:

* the error doesn’t appear on my internal pages (ie pamblizzard.com/connect) and those pages display appropriately including WC pages, /cart and /shop display just fine

Fatal Error (hide details) (remove)
The site encountered a problem that it cannot recover from. Please use the following information to try to resolve the problem.

Error Message

Fatal Error: Call to undefined function is_cart() in /nas/content/live/pamblizzard/wp-content/plugins/woocommerce-gateway-paypal-powered-by-braintree/woocommerce-gateway-paypal-powered-by-braintree.php on line 514
Description

The WooCommerce PayPal Powered by Braintree Gateway plugin code created an error that caused PHP execution to fail.

The code tried to run a function that doesn’t exist (is_cart()). This type of error is typically caused by a simple typo (is_hom() rather than is_home()), by calling a function provided by a plugin when that plugin is not activated, by calling a function before it is ready (such as calling a function before the code that creates it has run), or by using a function that no longer exists (the function may have been removed from WordPress core or the plugin/theme that previously supplied it).

Solutions

Invalid code modifications can cause this problem. If you have made any modifications to the plugin, remove them and try to load the site again.
It is possible that this plugin’s code is out of date and that an upgrade is available. Check with the plugin’s author to see if an upgrade is available.
There may be a conflict with another plugin running on the site. Try upgrading the other plugins on the site. A plugin conflict can be ruled out by deactivating all the other active plugins on the site and checking to see if the error still occurs.
The WooCommerce PayPal Powered by Braintree Gateway plugin may not have been fully uploaded. Uploading the plugin again could fix the issue. Important: If you do this, you will lose any modifications made to the plugin.
Error Source Details

Type Plugin
Name WooCommerce PayPal Powered by Braintree Gateway
Version 1.2.0
Author WooThemes
Path /nas/content/live/pamblizzard/wp-content/plugins/woocommerce-gateway-paypal-powered-by-braintree
File woocommerce-gateway-paypal-powered-by-braintree.php
Other Software Details

WordPress Version 4.5.1
PHP Version 5.5.9-1ubuntu4.14
Full Error Details

Type Fatal Error (E_ERROR)
Message Call to undefined function is_cart()
File /nas/content/live/pamblizzard/wp-content/plugins/woocommerce-gateway-paypal-powered-by-braintree/woocommerce-gateway-paypal-powered-by-braintree.php
Line 514
Type Description This type of error indicates that PHP cannot continue to run the code. Typical causes of this type of error are code bugs that have typos, missing or incomplete files (such as a file that was only partially uploaded), and the code using more memory than it is allowed.

Note that this message is generated by iThemes.com products when an error is encountered on the site. While an iThemes product is generating this message, it is not necessarily the cause of the problem.

Please advise what I can do to eliminate this.

https://www.ads-software.com/plugins/woocommerce-gateway-paypal-powered-by-braintree/