Index: CKEditor/trunk/_source/plugins/styles/plugin.js
===================================================================
--- CKEditor/trunk/_source/plugins/styles/plugin.js	(revision 6818)
+++ CKEditor/trunk/_source/plugins/styles/plugin.js	(revision 6820)
@@ -816,5 +816,5 @@
 		var root = range.getCommonAncestor( true, true ),
 			element = root.getAscendant( this.element, true );
-		element && setupElement( element, this );
+		element && !element.isReadOnly() && setupElement( element, this );
 	}
 
@@ -873,6 +873,9 @@
 		while ( ( block = iterator.getNextParagraph() ) )		// Only one =
 		{
-			var newBlock = getElement( this, doc, block );
-			replaceBlock( block, newBlock );
+			if ( !block.isReadOnly() )
+			{
+				var newBlock = getElement( this, doc, block );
+				replaceBlock( block, newBlock );
+			}
 		}