Extended Core Class not Loading on server.

[eluser]ironlung[/eluser]
Hi I have an extended core class MY_Lang.php, which loads perfectly well at home on my mamp server but not on my hosting server.

After an age I decided to hack common.php load_class and find out what was going on. I could see it checking for application/core/MY_Lang.php and failing the check so:

1) I placed a file fred.txt and put in a check to find that in common.php, all fine, it found it.
2) I changed the filename to Fred.txt and changed the check in common.php to check for that filename and it fails.

Does anyone have any idea what's going on on my host server and what I can do to sort it out please?