Error: Use of undefined constant in PHP

Hello friends,
I got this error message & I dont understand why I am getting this error message without any changes been made from my side.

Error: Use of undefined constant

It says something like:

Code:

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Notice: Use of undefined constant ID_my_site - assumed 'ID_my_site' in /path/.../login.php on line 70

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Can you let me know what should I do?

Notice: Use of undefined constant/variable
Due to a change of requirements between php versions, it became necessary to define and/or initialize all the constants and variables used in php

The work-round to this issue is to change the php.ini settings from

Code:

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error_reporting = E_ALL

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to

Code:

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error_reporting = E_ALL & ~E_NOTICE

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Here It is the Answer to your Question
Predefined Variables
PHP provides a large number of predefined variables to any script which it runs. Many of these variables, however, cannot be fully documented as they are dependent upon which server is running, the version and setup of the server, and other factors.
From version 4.1.0 onward, PHP provides an additional set of predefined arrays containing variables from the web server (if applicable), the environment, and user input. These new arrays are rather special in that they are automatically global--i.e., automatically available in every scope. For this reason, they are often known as "superglobals". (There is no mechanism in PHP for user-defined superglobals.)
Superglobals cannot be used as variable variables inside functions or class methods.
http://www.php.net/manual/en/languag...predefined.php

I hope this helps you.

I am working with Joomla & PHP.
I just got updated to the latest version.
Now I see an error message in my log message:

Code:

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PHP Notice:  Use of undefined constant _ISO - assumed '_ISO' in /home/mysite/public_html/Portal/includes/joomla.php on line 2651

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What do you suggest me?