From the horses mouth, well the xcart faq anyway ...

Q : While ruuning X-Cart I get the following error messages:
Warning: MkDir failed (Permission denied) in /u/http/user/xcart/Smarty-2.0/Smarty.class.php on line 1366
Warning: Smarty error: problem creating directory "../templates_c/-20/-2087024569" in /u/http/user/xcart/Smarty-2.0/Smarty.class.php on line 470
Warning: Smarty error: problem writing '../temp8lates_c/-20/-2087024569/0.php.' in /u/http/user/xcart/Smarty-2.0/Smarty.class.php on line 470
Warning: Failed opening '../templates_c/-20/-2087024569/0.php' for inclusion (include_path='.:/usr/local/lib/php4/lib/php') in /u/http/user/xcart/Smarty-2.0/Smarty.class.php on line 1003

A : The "templates_c" directory contains cache of compiled templates.
These errors occur because web server has no enough permissions to overwrite temporary cache files in directory templates_c. You probably have copied them while moving X-Cart and these files now do not belong to web server user (httpd or nobody). To fix this issue just remove all your files from that directory. Everything will be recreated by Smarty. Also, this directory must have writeable permissions, which can be achieved by "chmod 777 templates_c" command.

I deleted all those files and it works. Thanks

Should these files be deleted every so often? Seems like they are just taking up space.

only gets messy if your updating / editing lots of files.

Once your done working on the site flush the templates_c and then all should be fine and not need empting again.

Once I'm DONE?! Ha!

i just installed 3.4.2 and noticed that my skin1 directory is 777 with owner = nobody. I tried to chmod this to 755 but i cannot because of the nobody owner. I cant chown the files either.

what do I need to do to change the permissions? i dont want 777 permissions on these !!!