Data Controls :: File Type And Extension Validation For Multiple File Upload Controls Using Custom Validator

I was referring muddasar's one of the article for the validation. Below is my code and i am trying to validate the file upload selected file format on the submit button. I have 4 upload control and  fu1 is mandatory field and others are not mandatory fields. Though i need to validate all the four uploads if the files have been selected. My full sample code is below for easy testing,

<asp:FileUpload runat="server" ID="fu1" />
<asp:Label ID="lblMessage1" runat="server"></asp:Label>
<asp:FileUpload runat="server" ID="fu2" />
<asp:Label ID="lblMessage2" runat="server"></asp:Label>

[code]...

I am doing slight mistake on the return to the main function. if i test indvidual function it works fine. whereas if i include the 4 functions in one function  with the return statement, it's not validating. goes to to the server.