Try recursively making your cache directory writable, e.g. call something like 'chmod -R 755 cache/' from your OCS directory.
I'm back on the trail of this, trying to upgrade both OCS and OJS to the latest. I just ran the chmod command against my ojs cache directory, and still no joy: I get a blank screen. My cache dir looks like this:
drwxr-xr-x 6 root root 4096 Mar 2 15:08 _db
drwxr-xr-x 2 root root 4096 Mar 2 15:08 t_cache
drwxr-xr-x 2 root root 16384 Mar 2 15:24 t_compile
drwxr-xr-x 2 root root 4096 Mar 2 15:08 t_config
And I'm still getting the same error about not being able to compile. (This, below, is from my attempted OJS upgrade, but it was the same with my OCS attempt):
Message: WARNING: Smarty::include() [<a href='function.include'>function.include</a>]: Failed opening '/var/www/html/ojs/cache/t_compile/%%7D^7DC^7DC17B21%%install.tpl.php
I am assuming it's trying to WRITE this *install.tpl.php file to the t_compile directory, but can't. And yet it looks like my permissions are correct, yes?