MVC :: How To Display Model Level Custom Data Annotation Validation Error

I am a MVC newbie & am lost in various ways validation can be implemented in my application.

I created a custom model-level data annotation validator attribute, but am unable to display its error message in the view. Basically, I have let's say 5 properties in the Entity class Job (model-level custom attribute called UniqueKeywords defined on it):

1) LoginID: value comes in the URL

2) Title: Required property level attribute defined on it

3) CatID1, CatID2, CatID3 - 3 categoryIDs - these are dropdowns in the view with same list of keywords in all 3.

I want to mandate that the values picked by the user in all 3 category dropdowns should be different.

With reference to the code pasted below, here is the explanation of what happens:

When I submit the form without specifying a title or picking anything from any of the 3 category dropdowns, the validation occurs for the property level Required attribute as well as model level uniquekeywords attribute, but the error is displayed only next to the required field "Title". I can confirm that the custom validation also works by filling in some text in the Title field & then re-posting the form...this re-displays the view, but the error message "Category cannot be duplicated" is not displayed.

Only relevant code sections are pasted below:

My Entity class code:

[Code]....