Some times after migration of magento you get strange behavior of magento i.e blank page or warning like

 Warning: simplexml_load_string()

That happens when magento tries to parse the xml config file most probably the config file of modules/extensions

Possible solutions:
1. check all the extensions are there in new installation
2. go to magento connect and check extensions status there
3. install all missing extensions

This will resolve your problem.

If not then open lib/Varien/Simple/Config.php

Search for function “loadFile” and echo the file path it will let you know the faulty xml configuration file.

Hope that helps.