Q:

Fatal error: Class ‘MagentoPycho_Lightboxes_Helper_Data’ not found in appMage.php on line 516

I am facing problem after installing jQuery Lightboxes (FancyBox, PiroBox etc.)
Fatal error: Class ‘MagentoPycho_Lightboxes_Helper_Data’ not found in appMage.php on line 516

[UPDATED] 
Some parameters in the js/colorswatch/colorswatch.js  (line 34) are undefined when Lightboxes are instaslled ( even if they are disabled ).
Here is my error message. in var\log\system.log: 

2013-03-01T10:05:02+00:00 ERR (3): Notice: Trying to get property of
  non-object  in
  D:\xampp\htdocs\store\includes\src\Mage_Adminhtml_Model_Config_Data.php
  on line 135 2013-03-01T10:05:02+00:00 ERR (3): Notice: Trying to get
  property of non-object  in
  D:\xampp\htdocs\store\includes\src\Mage_Adminhtml_Model_Config_Data.php
  on line 135 2013-03-01T10:05:09+00:00 ERR (3): Notice: Undefined
  variable: productId  in
  D:\xampp\htdocs\store\app\design\frontend\default\helloresponsive\template\catalog\product\compare\sidebar.phtml
  on line 32 2013-03-01T10:05:17+00:00 ERR (3): Notice: Undefined
  variable: productId  in
  D:\xampp\htdocs\store\app\design\frontend\default\helloresponsive\template\catalog\product\compare\sidebar.phtml
  on line 32 2013-03-01T10:05:22+00:00 ERR (3): Notice: Undefined
  variable: productId  in
  D:\xampp\htdocs\store\app\design\frontend\default\helloresponsive\template\catalog\product\compare\sidebar.phtml
  on line 32

This function  $this->getGroups() is not returning anything. 

A:

First of all make sure it's not your cache or compile.
Then check have app/code/local/MagentoPycho/Lightboxes/Helper/Data.php file in place and there's MagentoPycho_Lightboxes_Helper_Data class inside.
If the problem is still there it is possible that you have another (same extension in another scope) which uses that same group mame (in your case lightboxes).

