Marketpress fatal error cannot use string offset as an array

I'm running marketpress in an ithemes builder child and I'm getting the following fatal error on the coupons page.

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: Cannot use string offset as an array in /home/snowball/public_html/wp-content/plugins/marketpress/marketpress.php on line 5607
Description

The MarketPress plugin code created an error that caused PHP execution to fail.

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It is possible that this plugin's code is out of date and that an upgrade is available.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 MarketPress 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 MarketPress
Version 2.6.2
Author Aaron Edwards (Incsub)
Path /home/snowball/public_html/wp-content/plugins/marketpress
File marketpress.php
Other Software Details

WordPress Version 3.4.1
PHP Version 5.2.17
Full Error Details

Type Fatal Error (E_ERROR)
Message Cannot use string offset as an array
File /home/snowball/public_html/wp-content/plugins/marketpress/marketpress.php
Line 5607
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.