### Eclipse Workspace Patch 1.0
#P xwiki-core
Index: src/main/resources/ApplicationResources.properties
===================================================================
--- src/main/resources/ApplicationResources.properties	(revision 32887)
+++ src/main/resources/ApplicationResources.properties	(working copy)
@@ -234,7 +234,7 @@
   <br/>Names must not start with a number or punctuation character. \
   <br/>Names must not start with the letters xml (or XML, or Xml, etc). \
   <br/>Names cannot contain spaces.
-
+propertyexists="Property {0} already exists"
 backtoedit=Back To Edit
 browsernoncompatible=Browser is non compatible!
 wysiwygeditor=WYSIWYG Editor
Index: src/main/java/com/xpn/xwiki/web/PropAddAction.java
===================================================================
--- src/main/java/com/xpn/xwiki/web/PropAddAction.java	(revision 32887)
+++ src/main/java/com/xpn/xwiki/web/PropAddAction.java	(working copy)
@@ -20,6 +20,9 @@
  */
 package com.xpn.xwiki.web;
 
+import java.util.ArrayList;
+import java.util.List;
+
 import javax.servlet.http.HttpServletResponse;
 
 import com.xpn.xwiki.XWiki;
@@ -60,7 +63,12 @@
         BaseClass bclass = doc.getxWikiClass();
         bclass.setName(doc.getFullName());
         if (bclass.get(propName) != null) {
-            // TODO: handle the error of the property already existing when we want to add a class property
+            context.put("message", "propertyexists");
+            List<String> params = new ArrayList<String>();
+            params.add(propName);
+            response.setStatus(HttpServletResponse.SC_BAD_REQUEST, context.getMessageTool().get(
+                "propertyexists", params));
+            return true;
         } else {
             MetaClass mclass = xwiki.getMetaclass();
             PropertyMetaClass pmclass = (PropertyMetaClass) mclass.get(propType);