I have upgraded my PHP from version 5.2.9 to 5.3.1 and have encountered the following with my codeigniter application:
Unable to locate the model you have specified: some_model
Codeigniter version 2.1, with HMVC extension Server: Centos 5
The model names are all in lower case and it is also loaded by calling their lower case letter. Everything used to work before the PHP upgrade.