diff --git a/common/lang/en.php b/common/lang/en.php
index 5f9b3325d..99dfc2c60 100644
--- a/common/lang/en.php
+++ b/common/lang/en.php
@@ -281,11 +281,18 @@ $lang->fail_to_registed = 'Failed to register.';
 $lang->fail_to_update = 'Fail to update.';
 $lang->fail_to_delete = 'Failed to delete.';
 $lang->fail_to_move = 'Failed to move.';
-$lang->failed_voted = 'No permission to upvote.';
+$lang->failed_voted = 'No permission to upvote this post.';
+$lang->failed_voted_already = 'You have already voted on this post.';
+$lang->failed_voted_self = 'You cannot upvote your own post.';
 $lang->failed_voted_canceled = 'You cannot cancel an upvote that you did\'t make.';
-$lang->failed_blamed = 'No permission to downvote.';
+$lang->failed_voted_cancel = 'You cannot cancel an upvote.';
+$lang->failed_blamed = 'No permission to downvote this post.';
+$lang->failed_blamed_self = 'You cannot downvote your own post.';
 $lang->failed_blamed_canceled = 'You cannot cancel a downvote that you did\'t make.';
-$lang->failed_declared = 'No permission to Report.';
+$lang->failed_blamed_cancel = 'You cannot cancel a downvote.';
+$lang->failed_declared = 'No permission to report this post.';
+$lang->failed_declared_already = 'You have already reported this post.';
+$lang->failed_declared_self = 'You cannot report your own post.';
 $lang->failed_declared_cancel = 'You cannot cancel the report.';
 $lang->fail_to_delete_have_children = 'Cannot delete the article with comments.';
 $lang->confirm_submit = 'Are you sure you want to submit?';
diff --git a/common/lang/ko.php b/common/lang/ko.php
index f605fed42..8aeeca919 100644
--- a/common/lang/ko.php
+++ b/common/lang/ko.php
@@ -284,11 +284,17 @@ $lang->fail_to_update = '수정하지 못했습니다.';
 $lang->fail_to_delete = '삭제 실패했습니다.';
 $lang->fail_to_move = '이동 실패했습니다.';
 $lang->failed_voted = '추천할 수 없습니다.';
+$lang->failed_voted_already = '이미 추천 또는 비추천한 게시물입니다.';
+$lang->failed_voted_self = '자신의 게시물을 추천할 수 없습니다.';
 $lang->failed_voted_canceled = '추천한 적이 없으므로 취소할 수 없습니다.';
 $lang->failed_voted_cancel = '추천을 취소할 수 없습니다.';
 $lang->failed_blamed = '비추천할 수 없습니다.';
+$lang->failed_blamed_self = '자신의 게시물을 비추천할 수 없습니다.';
 $lang->failed_blamed_canceled = '비추천한 적이 없으므로 취소할 수 없습니다.';
+$lang->failed_blamed_cancel = '비추천을 취소할 수 없습니다.';
 $lang->failed_declared = '신고할 수 없습니다.';
+$lang->failed_declared_already = '이미 신고한 게시물입니다.';
+$lang->failed_declared_self = '자신의 게시물을 신고할 수 없습니다.';
 $lang->failed_declared_cancel = '신고를 취소할 수 없습니다.';
 $lang->fail_to_delete_have_children = '댓글이 있어서 삭제할 수 없습니다.';
 $lang->confirm_submit = '등록하시겠습니까?';
diff --git a/modules/comment/comment.controller.php b/modules/comment/comment.controller.php
index 27c243016..195ce2f70 100644
--- a/modules/comment/comment.controller.php
+++ b/modules/comment/comment.controller.php
@@ -266,7 +266,8 @@ class CommentController extends Comment
 
 	function updateVotedCountCancel($comment_srl, $oComment, $point)
 	{
-		if(!$_SESSION['voted_comment'][$comment_srl] && !$this->user->member_srl)
+		// Guests can only cancel votes that are registered in the current session.
+		if(!$this->user->member_srl && empty($_SESSION['voted_comment'][$comment_srl]))
 		{
 			return new BaseObject(-1, $point > 0 ? 'failed_voted_canceled' : 'failed_blamed_canceled');
 		}
@@ -1568,9 +1569,9 @@ class CommentController extends Comment
 		}
 
 		// invalid vote if vote info exists in the session info.
-		if($_SESSION['voted_comment'][$comment_srl])
+		if(!empty($_SESSION['voted_comment'][$comment_srl]))
 		{
-			return new BaseObject(-1, $failed_voted);
+			return new BaseObject(-1, $failed_voted . '_already');
 		}
 
 		// Get the original comment
@@ -1592,7 +1593,7 @@ class CommentController extends Comment
 			if($member_srl && $member_srl == abs($oComment->get('member_srl')))
 			{
 				$_SESSION['voted_comment'][$comment_srl] = false;
-				return new BaseObject(-1, $failed_voted);
+				return new BaseObject(-1, $failed_voted . '_self');
 			}
 		}
 
@@ -1687,9 +1688,9 @@ class CommentController extends Comment
 	function declaredComment($comment_srl, $declare_message)
 	{
 		// Fail if session information already has a reported document
-		if(isset($_SESSION['declared_comment'][$comment_srl]))
+		if(!empty($_SESSION['declared_comment'][$comment_srl]))
 		{
-			return new BaseObject(-1, 'failed_declared');
+			return new BaseObject(-1, 'failed_declared_already');
 		}
 
 		// check if already reported
@@ -1738,7 +1739,7 @@ class CommentController extends Comment
 			if($member_srl && $member_srl == abs($oComment->get('member_srl')))
 			{
 				$_SESSION['declared_comment'][$comment_srl] = FALSE;
-				return new BaseObject(-1, 'failed_declared');
+				return new BaseObject(-1, 'failed_declared_self');
 			}
 		}
 
@@ -1757,7 +1758,7 @@ class CommentController extends Comment
 		if($log_output->data->count)
 		{
 			$_SESSION['declared_comment'][$comment_srl] = FALSE;
-			return new BaseObject(-1, 'failed_declared');
+			return new BaseObject(-1, 'failed_declared_already');
 		}
 
 		// Fill in remaining information for logging.
diff --git a/modules/document/document.controller.php b/modules/document/document.controller.php
index caf03fbfb..dfe23d2a8 100644
--- a/modules/document/document.controller.php
+++ b/modules/document/document.controller.php
@@ -285,7 +285,8 @@ class DocumentController extends Document
 	 */
 	function updateVotedCountCancel($document_srl, $oDocument, $point)
 	{
-		if(!$_SESSION['voted_document'][$document_srl] && !$this->user->member_srl)
+		// Guests can only cancel votes that are registered in the current session.
+		if(!$this->user->member_srl && empty($_SESSION['voted_document'][$document_srl]))
 		{
 			return new BaseObject(-1, $point > 0 ? 'failed_voted_canceled' : 'failed_blamed_canceled');
 		}
@@ -1800,9 +1801,9 @@ class DocumentController extends Document
 		}
 
 		// Return fail if session already has information about votes
-		if($_SESSION['voted_document'][$document_srl])
+		if(!empty($_SESSION['voted_document'][$document_srl]))
 		{
-			return new BaseObject(-1, $failed_voted);
+			return new BaseObject(-1, $failed_voted . '_already');
 		}
 
 		// Get the original document
@@ -1824,7 +1825,7 @@ class DocumentController extends Document
 			if($member_srl && $member_srl == abs($oDocument->get('member_srl')))
 			{
 				$_SESSION['voted_document'][$document_srl] = false;
-				return new BaseObject(-1, $failed_voted);
+				return new BaseObject(-1, $failed_voted . '_self');
 			}
 		}
 
@@ -1931,9 +1932,9 @@ class DocumentController extends Document
 	function declaredDocument($document_srl, $declare_message = '')
 	{
 		// Fail if session already tried to report the document
-		if(isset($_SESSION['declared_document'][$document_srl]))
+		if(!empty($_SESSION['declared_document'][$document_srl]))
 		{
-			return new BaseObject(-1, 'failed_declared');
+			return new BaseObject(-1, 'failed_declared_already');
 		}
 
 		// Check if previously reported
@@ -1982,7 +1983,7 @@ class DocumentController extends Document
 			if($member_srl && $member_srl == abs($oDocument->get('member_srl')))
 			{
 				$_SESSION['declared_document'][$document_srl] = false;
-				return new BaseObject(-1, 'failed_declared');
+				return new BaseObject(-1, 'failed_declared_self');
 			}
 		}
 
@@ -2001,7 +2002,7 @@ class DocumentController extends Document
 		if($output->data->count)
 		{
 			$_SESSION['declared_document'][$document_srl] = false;
-			return new BaseObject(-1, 'failed_declared');
+			return new BaseObject(-1, 'failed_declared_already');
 		}
 
 		// Fill in remaining information for logging.