TYPO3 Core

Hi according to TYPO3 Core APIs guide to clear FE cache I must to call
$tce->clear_cacheCmd('<value>')

this could be an integer or pages/all/temp_CACHED

when I attempt to use it from my extension (ttnews_feeder) and pass to it as parameter one or more pids all is fine, but when I run:

$tce->clear_cacheCmd('pages') from BE the extension is 'blocked'; TYPO3 can't access to any page (results in: page not found).

The error log reports this FATAL ERROR:

[Mon Dec 24 11:51:29 2007] [error] [client 195.210.65.21] PHP Fatal error: Call to a member function getTSConfigVal() on a non-object in /var/www/typo3_src-4.1.4/t3lib/class.t3lib_tcemain.php on line 6156, referer: http://www.bandamadrisio.it/typo3/alt_mod_frameset.php?fW=0&nav=/typo3/alt_db_navframe.php%3F&script=..%2Ftypo3conf%2Fext%2Fttnews_feeder%2Fmod1%2Findex.php&id=

If a numerica value (i tested if integer) is passed there are no problems; if passed the code above 'pages' all blocks.
(issue imported from #M7042)