Cannot redeclare class CI_Exceptions

[eluser]shane_[/eluser]
I've suddenly started getting a fatal error involving 'Cannot redeclare class CI_Exceptions.' The application has been running for about a year without any issues. It turns out that I had extended the Exceptions class several months ago. So when I removed the subclass the issue goes away. I'm not sure what has changed recently, anyone know what could have brought this on suddenly? It's CI version 1.7.2.