Pushing inode limit
What version of C5 are you running?
But unless you have a ludicrous number of files in your file manager, it's unlikely to be the cause of your inode limit being reached.
I think nearly every time I've seen this is when temporary session files aren't being automatically cleaned up (often called 'garbage collection'), and these grow in number over time.
When this has happened it's been because the PHP install hasn't been configured correctly/completely. Turning the garbage collection on either at the master config level, or an account level with some settings like these in an .htaccess file have worked for me:
php_value session.gc_divisor 100 php_value session.gc_probability 1
Adding these in and visiting the site a few times kicks this process off and the number of session files drops back down to a normal level.
Besides that suggestion sometimes the cache folder can get very large, but I don't ever recall hitting inode limits because of it.
Also note that the inode count in cPanel isn't going to update immediately, I believe there's a nightly script that runs to update that count.