TYPO3 Core

I think more info is necessary here.

Is this a fresh install or an upgrade from an older version?

What extensions are installed?

How does $GLOBALS['TYPO3_CONF_VARS']['SYS']['caching']['cacheConfigurations'] look like?

This is an upgrade install from TYPO3 6.1 where this error message did never shop up.

The extensions tt_products and party have been installed. In the EM for tt_products the [cache.cache.backend] is empty.
The file ext_localconf.php of tt_products sets the Caching Framework.
Sometimes it happens that the class t3lib_cache_backend_NullBackend is not found.

$typoVersion = tx_div2007_core::getTypoVersion();

// support for new Caching Framework

$optionsArray = array();
$backendCache = 't3lib_cache_backend_NullBackend';

// Register cache 'tt_products_cache'
if (
    isset($_EXTCONF['cache.']) &&
    $_EXTCONF['cache.']['backend'] &&
    !is_array($GLOBALS['TYPO3_CONF_VARS']['SYS']['caching']['cacheConfigurations']['tt_products_cache'])
) {
    if (
        isset($_EXTCONF['cache.']['options.']) &&
        $_EXTCONF['cache.']['options.']['servers'] != ''
    ) {
        $optionsArray['servers'] = array($_EXTCONF['cache.']['options.']['servers']);
    }

    if (
        extension_loaded('memcache') &&
        isset($optionsArray['servers']) &&
        is_array($optionsArray['servers'])
    ) {
        $backendCache = 't3lib_cache_backend_MemcachedBackend';
    } else if (extension_loaded('apc') || extension_loaded('apcu')) {
        $backendCache = 't3lib_cache_backend_ApcBackend';
    } else if (extension_loaded('redis')) {
        $backendCache = 't3lib_cache_backend_RedisBackend';
    }
}

if (!isset($GLOBALS['TYPO3_CONF_VARS']['SYS']['caching']['cacheConfigurations']['tt_products_cache'])) {
    $GLOBALS['TYPO3_CONF_VARS']['SYS']['caching']['cacheConfigurations']['tt_products_cache'] = array();
}

// Define string frontend as default frontend, this must be set with TYPO3 4.5 and below
// and overrides the default variable frontend of 4.6
if (!isset($TYPO3_CONF_VARS['SYS']['caching']['cacheConfigurations']['tt_products_cache']['frontend'])) {
    $TYPO3_CONF_VARS['SYS']['caching']['cacheConfigurations']['tt_products_cache']['frontend'] = 't3lib_cache_frontend_StringFrontend';
}

if ($typoVersion >= '4006000') {

    if (!isset($TYPO3_CONF_VARS['SYS']['caching']['cacheConfigurations']['tt_products_cache']['backend'])) {
        $TYPO3_CONF_VARS['SYS']['caching']['cacheConfigurations']['tt_products_cache']['backend'] = $backendCache;
    }

    if (!isset($TYPO3_CONF_VARS['SYS']['caching']['cacheConfigurations']['tt_products_cache']['options'])) {
        $TYPO3_CONF_VARS['SYS']['caching']['cacheConfigurations']['tt_products_cache']['options'] = $optionsArray;
    }
}

if ($typoVersion < '4006000') {
    // Define database backend as backend for 4.5 and below (default in 4.6)
    if (!isset($TYPO3_CONF_VARS['SYS']['caching']['cacheConfigurations']['tt_products_cache']['backend'])) {
        $TYPO3_CONF_VARS['SYS']['caching']['cacheConfigurations']['tt_products_cache']['backend'] = 't3lib_cache_backend_DbBackend';
    }
    // Define data and tags table for 4.5 and below (obsolete in 4.6)
    if (!isset($TYPO3_CONF_VARS['SYS']['caching']['cacheConfigurations']['tt_products_cache']['options'])) {
        $TYPO3_CONF_VARS['SYS']['caching']['cacheConfigurations']['tt_products_cache']['options'] = array();
    }
    if (!isset($TYPO3_CONF_VARS['SYS']['caching']['cacheConfigurations']['tt_products_cache']['options']['cacheTable'])) {
        $TYPO3_CONF_VARS['SYS']['caching']['cacheConfigurations']['tt_products_cache']['options']['cacheTable'] = 'tt_products_cache';
    }
    if (!isset($TYPO3_CONF_VARS['SYS']['caching']['cacheConfigurations']['tt_products_cache']['options']['tagsTable'])) {
        $TYPO3_CONF_VARS['SYS']['caching']['cacheConfigurations']['tt_products_cache']['options']['tagsTable'] = 'tt_products_cache_tags';
    }

    t3lib_cache::initializeCachingFramework();
} else {
    // add missing setup for the tt_content "list_type = 5" which is used by tt_products
    $addLine = 'tt_content.list.20.5 = < plugin.tt_products';
    t3lib_extMgm::addTypoScript(TT_PRODUCTS_EXT, 'setup', '
    # Setting ' . TT_PRODUCTS_EXT . ' plugin TypoScript
    ' . $addLine . '
    ', 43);
}

if (
    isset($GLOBALS['typo3CacheFactory']) &&
    is_object($GLOBALS['typo3CacheFactory']) &&
    ($typoVersion >= '4006000' || TYPO3_UseCachingFramework)
) {
    // register the cache in BE so it will be cleared with "clear all caches" 
    try {
        $GLOBALS['typo3CacheFactory']->create(
            'tt_products_cache',
            $GLOBALS['TYPO3_CONF_VARS']['SYS']['caching']['cacheConfigurations']['tt_products_cache']['frontend'],
            $GLOBALS['TYPO3_CONF_VARS']['SYS']['caching']['cacheConfigurations']['tt_products_cache']['backend'],
            $GLOBALS['TYPO3_CONF_VARS']['SYS']['caching']['cacheConfigurations']['tt_products_cache']['options']);
    } catch (t3lib_cache_exception_DuplicateIdentifier $e) {
        // do nothing, a tt_products_cache cache already exists
    }
}