>>>>>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
>>>>
>>>>Do you have both scripts included into the master page ? (jQuery and plug-in)?
>>>
>>>Yes, I have both scripts in the master page. And I also tried to add these scripts on a page where I use them. But to no avail.
>>
>>Make sure they are included in the right order and also try refreshing everything. I think I had similar problems when one of the scripts was not correctly loaded.
>
>I did double check this.

Check the network tab in the debugger I just told you about and see if there is an error loading the js files.