Problems after php 5.3 update

Greetings!

While updating a plugin, it required php 5.3, so when I changed the php version and went to manage templates>you events, I found out that the item headings and descriptions all appear with underscores STYLE_SETTINGS_TAB, CUSTOM_CSS_SLABEL, and so on.

I tried to find out what happened, until I reverted to php 5.2, then the headings and descriptions looked normal, but then when I go to visit the website, it returns an Error 500. The site will only be loaded when I go back to using php 5.3.

Did anyone ever experience this?

Thanks a lot in advance for any advice on the matter.

Are you sure your are posting in product assigned forum?: No

What is your CMS version?: Joomla 2.5

MySQL Version: 5.x

PHP version: 5.x

Link to installation: Qatar Entertainer - Qatar Entertainer

Have you edited any files? If yes tell us which ones.: N/A

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I don't know what membership we have. But I am able to login and download member's only products.