$force_compile set to true should force all templates to be compiled regardless of timestamp. This should fix the problem, unless you have improper permissions on the templates_c/ dir, I'd remove the directory and let smarty recreate it so it has permissions the webserver can read/write too.
Another thing I would change is:
$smarty->use_sub_dirs = false;
in smarty.php, I don't see the point of forcing compiling in one dir?
Btw, caching is disabled by default in x-cart with smarty.
$caching = 0;
hth.
