diff --git a/redback-integrations/redback-rest/redback-rest-api/src/main/java/org/apache/archiva/redback/rest/api/Constants.java b/redback-integrations/redback-rest/redback-rest-api/src/main/java/org/apache/archiva/redback/rest/api/Constants.java
index 54a03e82..0d0697ea 100644
--- a/redback-integrations/redback-rest/redback-rest-api/src/main/java/org/apache/archiva/redback/rest/api/Constants.java
+++ b/redback-integrations/redback-rest/redback-rest-api/src/main/java/org/apache/archiva/redback/rest/api/Constants.java
@@ -37,6 +37,7 @@ public interface Constants
     String ERR_USER_ID_INVALID = "redback:user.id.invalid";
     String ERR_USER_FULL_NAME_EMPTY = "redback:user.fullname.empty";
     String ERR_USER_EMAIL_EMPTY = "redback:user.email.empty";
+    String ERR_USER_EMAIL_INVALID = "redback:user.email.invalid";
     String ERR_USER_ASSIGN_ROLE = "redback:user.role.assign.failure";
     String ERR_USER_NOT_VALIDATED = "redback:user.not_validated";
     String ERR_USER_ADMIN_EXISTS = "redback:user.admin.exists";
diff --git a/redback-integrations/redback-rest/redback-rest-services/src/main/java/org/apache/archiva/redback/rest/services/v2/DefaultUserService.java b/redback-integrations/redback-rest/redback-rest-services/src/main/java/org/apache/archiva/redback/rest/services/v2/DefaultUserService.java
index d7c64b3d..53a4fb2d 100644
--- a/redback-integrations/redback-rest/redback-rest-services/src/main/java/org/apache/archiva/redback/rest/services/v2/DefaultUserService.java
+++ b/redback-integrations/redback-rest/redback-rest-services/src/main/java/org/apache/archiva/redback/rest/services/v2/DefaultUserService.java
@@ -940,29 +940,29 @@ public void validateCredentialsLoose( User user )
             new RedbackServiceException( "issues during validating user", 422 );
         if ( StringUtils.isEmpty( user.getUserId() ) )
         {
-            redbackServiceException.addErrorMessage( new ErrorMessage( "username.required", null ) );
+            redbackServiceException.addErrorMessage( ErrorMessage.of( ERR_USER_ID_EMPTY ) );
         }
         else
         {
             if ( !user.getUserId().matches( VALID_USERNAME_CHARS ) )
             {
-                redbackServiceException.addErrorMessage( new ErrorMessage( "username.invalid.characters", null ) );
+                redbackServiceException.addErrorMessage( ErrorMessage.of( ERR_USER_ID_INVALID ) );
             }
         }
 
         if ( StringUtils.isEmpty( user.getFullName() ) )
         {
-            redbackServiceException.addErrorMessage( new ErrorMessage( "fullName.required", null ) );
+            redbackServiceException.addErrorMessage( ErrorMessage.of( ERR_USER_FULL_NAME_EMPTY ) );
         }
 
         if ( StringUtils.isEmpty( user.getEmail() ) )
         {
-            redbackServiceException.addErrorMessage( new ErrorMessage( "email.required", null ) );
+            redbackServiceException.addErrorMessage( ErrorMessage.of( ERR_USER_EMAIL_EMPTY ) );
         }
 
         if ( !StringUtils.equals( user.getPassword(), user.getConfirmPassword() ) )
         {
-            redbackServiceException.addErrorMessage( new ErrorMessage( "passwords.do.not.match", null ) );
+            redbackServiceException.addErrorMessage( ErrorMessage.of( ERR_AUTH_INVALID_CREDENTIALS, "nomatch" ) );
         }
 
         try
@@ -974,7 +974,7 @@ public void validateCredentialsLoose( User user )
         }
         catch ( AddressException e )
         {
-            redbackServiceException.addErrorMessage( new ErrorMessage( "email.invalid", null ) );
+            redbackServiceException.addErrorMessage( ErrorMessage.of( ERR_USER_EMAIL_INVALID ) );
         }
         if ( !redbackServiceException.getErrorMessages().isEmpty() )
         {
@@ -997,12 +997,12 @@ public void validateCredentialsStrict( User user )
 
             if ( ( StringUtils.isEmpty( user.getPassword() ) ) )
             {
-                throw new RedbackServiceException( new ErrorMessage( "password.required", null ) );
+                throw new RedbackServiceException( ErrorMessage.of( ERR_AUTH_INVALID_CREDENTIALS, "empty" ) );
             }
         }
         catch ( UserManagerException e )
         {
-            throw new RedbackServiceException( new ErrorMessage( e.getMessage() ) );
+            throw new RedbackServiceException( ErrorMessage.of( ERR_AUTH_INVALID_CREDENTIALS, e.getMessage() ) );
         }
     }
 
@@ -1046,7 +1046,7 @@ private org.apache.archiva.redback.users.User updateUser( String userId, Functio
         }
         catch ( UserManagerException e )
         {
-            throw new RedbackServiceException( new ErrorMessage( e.getMessage() ) );
+            throw new RedbackServiceException( ErrorMessage.of( ERR_USERMANAGER_FAIL, e.getMessage() ) );
         }
     }