Getting error warning when I submit Questions

My local server installation of   D W question & Answer plugin  triggers the following error message while submitting questions.
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Notice: Trying to get property of non-object in D:\wamp\www\skiaxpro\wp-content\plugins\dw-question-answer\inc\User.php on line 152
Notice: Trying to get property of non-object in D:\wamp\www\skiaxpro\wp-content\plugins\dw-question-answer\inc\User.php on line 152
Warning: Cannot modify header information – headers already sent by (output started at D:\wamp\www\skiaxpro\wp-content\plugins\dw-question-answer\inc\User.php:152) in D:\wamp\www\skiaxpro\wp-includes\pluggable.php on line 1210
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I installed the plugin on my live site also . Same problem occurs there too.
 The WordPress version that I am using is : 4.8.1 
Please help me resolve this issue.
Binu