It works on some installations and then it completely falls over on others.
Yes, it's the usual
Fatal error: Class 'Mage_Install_Controller_Router_Install' not found
Warning: include(Mage/Install/Controller/Router/Install.php) [function.include]:failed to open stream: No such file or directory
No compiler is not and has not been enabled
Yes the files exists
Yes rm -fr cache
Yes the permissions are correct
No there is no other server cache that needs updating
Yes disabled all other modules
Yes checked local/Mage directory
Any other suggestions?
Reverted back to the previous config.xml files for the moment whilst I put the kettle on.