diff --git a/code/CMSMain.php b/code/CMSMain.php
index fe99fd9c..51dac639 100644
--- a/code/CMSMain.php
+++ b/code/CMSMain.php
@@ -847,12 +847,16 @@ JS;
 		$record = $page->compareVersions($fromVersion, $toVersion);
 		$fromVersionRecord = Versioned::get_version('SiteTree', $id, $fromVersion);
 		$toVersionRecord = Versioned::get_version('SiteTree', $id, $toVersion);
+		if(!$fromVersionRecord) user_error("Can't find version $fromVersion of page $id", E_USER_ERROR);
+		if(!$toVersionRecord) user_error("Can't find version $toVersion of page $id", E_USER_ERROR);
 		
 		if($record) {
 			$fromDateNice = $fromVersionRecord->obj('LastEdited')->Ago();
 			$toDateNice = $toVersionRecord->obj('LastEdited')->Ago();
 			$fromAuthor = DataObject::get_by_id('Member', $fromVersionRecord->AuthorID);
+			if(!$fromAuthor) $fromAuthor = new ArrayData(array('Title' => 'Unknown author'));
 			$toAuthor = DataObject::get_by_id('Member', $toVersionRecord->AuthorID);
+			if(!$toAuthor) $toAuthor = new ArrayData(array('Title' => 'Unknown author'));
 
 			$fields = $record->getCMSFields($this);
 			$fields->push(new HiddenField("ID"));
diff --git a/code/Diff.php b/code/Diff.php
index 935ad810..ef2825e6 100755
--- a/code/Diff.php
+++ b/code/Diff.php
@@ -664,9 +664,12 @@ class Diff
 		// First split up the content into words and tags
 		$set1 = self::getHTMLChunks($from);
 		$set2 = self::getHTMLChunks($to);
-		
+				
 		// Diff that
 		$diff = new Diff($set1, $set2);
+
+		$tagStack[1] = $tagStack[2] = 0;
+		$rechunked[1] = $rechunked[2] = array();
 		
 		// Go through everything, converting edited tags (and their content) into single chunks.  Otherwise
 		// the generated HTML gets crusty
@@ -704,12 +707,12 @@ class Diff
 				if($chunks) {
 					foreach($chunks as $item) {
 						// $tagStack > 0 indicates that we should be tag-building
-						if(isset($tagStack[$listName])) $rechunked[$listName][sizeof($rechunked[$listName])-1] .= ' ' . $item;
+						if($tagStack[$listName]) $rechunked[$listName][sizeof($rechunked[$listName])-1] .= ' ' . $item;
 						else $rechunked[$listName][] = $item;
 	
 						if($lookForTag && isset($item[0]) && $item[0] == "<" && substr($item,0,2) != "</") {
 							$tagStack[$listName] = 1;
-						} else if(isset($tagStack[$listName])) {
+						} else if($tagStack[$listName]) {
 							if(substr($item,0,2) == "</") $tagStack[$listName]--;
 							else if(isset($item[0]) && $item[0] == "<") $tagStack[$listName]++;
 						}
@@ -719,7 +722,6 @@ class Diff
 				}
 			}
 		}
-
 		
 		// Diff the re-chunked data, turning it into maked up HTML
 		$diff = new Diff($rechunked[1], $rechunked[2]);
diff --git a/css/cms_left.css b/css/cms_left.css
index 73155920..89886a6c 100644
--- a/css/cms_left.css
+++ b/css/cms_left.css
@@ -394,15 +394,14 @@ ul.tree span.untranslated a:visited {
 	width: 70%;
 }
 
+/* Change detection CSS */
 #right ins, #right ins * {
-	background-color: green;
-	color: white;
+	background-color: #99EE66;
 	text-decoration: none;
 }
 
 #right del, #right del *{
-	background-color: red;
-	color: white;
+	background-color: #FF9999;
 	text-decoration: strikethough;
 }