PHP notice

Trying to get property of non-object

/var/www/application/controllers/survey/index.php(380)

368 }
369 if ($tokensexist == 1 && isset($token) && $token!="" && tableExists("{{tokens_".$surveyid."}}") && !$previewmode) //check if token is in a valid time frame
370 {
371 // check also if it is allowed to change survey after completion
372 if ($thissurvey['alloweditaftercompletion'] == 'Y' ) {
373 $tokenInstance = Token::model($surveyid)->editable()->findByAttributes(array('token' => $token));
374 } else {
375 $tokenInstance = Token::model($surveyid)->usable()->incomplete()->findByAttributes(array('token' => $token));
376 }
377 if (!isset($tokenInstance))
378 {
379 $tk = Token::model($surveyid)->findByAttributes(array('token' => $token));
380 if($tk->completed == 'N')
381 {
382 $now = dateShift(date("Y-m-d H:i:s"), "Y-m-d H:i:s", Yii::app()->getConfig("timeadjust"));
383 if(strtotime($now) < strtotime($tk->validfrom))
384 {
385 $err = $clang->gT("This invitation is not valid yet.");
386 }
387 else
388 {
389 $err = $clang->gT("This invitation is not valid anymore.");
390 }
391 }
392 else

Stack Trace
#0
–
/var/www/application/controllers/survey/index.php(47): index->action()

42 App()->getClientScript()->render($buffer);
43 App()->getClientScript()->reset();
44 return $buffer;
45 });
46 ob_implicit_flush(false);
47 $this->action();
48 ob_flush();
49 }
50
51 function action()
52 {