This is probably being caused by one of three things:
Ensure that the permissions on the directories 'cache' and 'templates_c' in resources/smarty/ are set to '777' (read/write/execute) for all users.
Try switching to the default design theme 'Charcoal' that comes with the software. If you've edited any of the template files that came with the script, make sure that your Smarty tags are correctly formatted with no mismatched curly braces.
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