Solve 'There was a problem‍​​ with reindexing process' Error in Magento

In Magento re-indexing is most important and useful functionality for rebuild all product data with any update in Magento website.because of this type of error you can't re-indexing website so it's problem in update information display in fronted or search functionality.
In Magento admin panel display index management message when you made any changes in website and that time re-indexing must require.Than you can click on that message or go to System->index Management for  re-indexing data.But sometimes when you try to re-indexing data from admin panel it's display error message like `There was a problem‍​​ with re-indexing process` and re-indexing process not complete. So don't worry it's simple solution here without any changing in database or any update.
First check here for solve basic steps and follow steps according to display there.if till not solve below error than it's problem in Magento database find database error in query re-indexing data using SSH or re-indexing by create new file as describe Here.Magento admin panel you can display database error by modifying changes in file `app/code/core/Mage/Index/controllers/Adminhtml/ProcessController.php` as below.

Mage::helper('index')->__('There was a problem with reindexing process.')

Replace this line with below code

Mage::helper('index')->__('There was a problem with reindexing process. ' . $e->getMessage())

Here just add `$e->getMessage()` for display SQL error in admin panel where display message. Check that error and try to solve according to your knowledge it's related to foreign key relation or any missing value in database tables. If you can't find any solution than repair database using `magento db repair tools`.for that just follow below steps.

1. Download Magento database repair tool from download page and unzip that
2. Put `magento-db-repair-tool-1.X.php` file in your Magento root directory
3. Backup your current Magento database to have ability to restore it if anything goes wrong
4. Install same version of Magento on server with same database prefix(If there is any Magento  database on same server without any error than no need to install new)
5. Now run db-repair file in URL http://SERVER_URL/PATH/magento-db-repair-tool-1.X.php
6. Here left side enter Magento database details which you want to repair and right side enter new database details where we install new Magento as below and click on `continue` button
7. If there is any error regarding `mysql_escape_string()` than replace `mysql_real_escape_string()` instead of that function and run again.

after run complete process clear all changes and try to re-indexing data it's run without any error. for more details for installation and support for Magento database repair tools in Magento 1.X click Here