What could be causing the "Fatal error: Cannot redeclare FastTemplate::clear_parse()" message in PHP when using the FastTemplate class?

The error "Fatal error: Cannot redeclare FastTemplate::clear_parse()" occurs when the FastTemplate class is being declared or included multiple times in the same script. To solve this issue, you need to check if the class has already been defined before declaring it again. This can be done using the `class_exists()` function in PHP.

if (!class_exists('FastTemplate')) {
    class FastTemplate {
        // Your class implementation here
    }
}