Marketing campaigns not sending email

I have the following version of the software that I am using with php 7.0.6.

Suite Version 7.5.3
Sugar Version 6.5.23 (Build 1061)

A test email from the admin console gets delivered to me without any issues. However, when I send an email from a marketing campaign, the email is stuck in the queue and never gets delivered to end user.

When I looked at the log file in suite crm installation directory, it says:
Tue May 24 10:20:00 2016 [9068][1][FATAL] Unable to return chart data, invalid xml for file cache/xml/9c17174c-fd42-8bd9-114f-573c716466e2_68e2abc7-ec40-08f9-2054-57430bca73c3.xml

I came across the following in the form: but the suggested fix is already present in the jschart,php file.

Can someone please help me fix this?