[TYPO3] tx_ratings rating extension

[Timothy Ding]

hello List,

while using tx_rating with tt_news, I see "Page is being generated.
... please reload", reloading the page several times sometimes bring
up the following fatal error.

Fatal error: Call to a member function sL() on a non-object in
/usr/local/typo3/htdocs/testsite/typo3conf/ext/ratings/class.tx_ratings_api.php
on line 247

is someone familiar with this or can tell me what can i do to fix it?
my system following versions of extension from TER.

ratings 1.0.7
tt_news 2.5.2
typo3 4.1.6

regards,
Tim