in Piwik 2.0.1 a “fatal error” was introduced. As I already described in Error when loading Log.php · Issue #4403 · matomo-org/matomo · GitHub the Log.php from the PEAR package instead of the Log.php in PIWIK_INCLUDE_PATH.’/core/’ is included in core/Error.php line 13. Depending on the configuration of your Server (include_path, open_basedir) this results in a fatal php error .
As error and solution (use full path to include Log.php in core/Error.php line 13) are pretty obvious to me I ommit explaining more details on this =)
Nontheless please feel free to ask, if you need more information.