If you have problem with including files
When Magento compilation is enabled, the following error messages are reported by Magento Connect Manager on a new extension installation:
ERR (3): Warning: include(Some_Magento_Code_Lib.php): failed to open stream: No such file or directory in includes/src/Varien_Autoload.php on line 93
ERR (3): Warning: include(): Failed opening 'Some_Magento_Code_Lib.php' for inclusion (include_path='includes/src:.') in includes/src/Varien_Autoload.php on line 93
To solve this you need to temporarily disable compilation at the System > Tools > Compilation screen in Magento Backend using the Disable button.
As soon as module installation is complete, you can enable compilation back at the same screen: System > Tools > Compilation.