>I am trying to incorporate into my project a masked input plug-in (URL: http://digitalbush.com/projects/masked-input-plugin/)
>
>When I add this .js
>

><script src="Scripts/jquery-1.7.1.js" type="text/javascript"></script>
><script src="Scripts/jquery.maskedinput-1.2.2.min.js" type="text/javascript"></script>
>

>to a separate .aspx file in my project, the mask() function works very well.
>
>But when I add it to a page that uses Master page, I get error:
>

>0x800a01b6 - Microsoft JScript runtime error: Object doesn't support property or method 'mask'
>

>
>The test code is identical in separate test page and the page that uses master page:
>
>

> <script type="text/javascript">
>        $(document).ready(function () {
>             $("#txtPhoneNumber").mask("(999) 9999-9999");
>        })
>    </script>
>

>
>The error (above) happens on the line .mask() above.
>
>How would you recommend to debug this situation? TIA

Looks as if the 'masked-input' js is not being loaded though from the info provided it's hard to know why not. Firstly use Chrome or IE development tools to find out what's happening. The 'Console' tab in Chrome should show whether it is attempting to load the file - and if it fails, why.....