Problem with GoogleTTS

I have installed properly GoogleTTS on Asterisk, but i have this error when i make a test

Launched AGI Script /var/lib/asterisk/agi-bin/googletts.agi
[2014-03-19 13:16:13] NOTICE[8315]: channel.c:4237 __ast_read: Dropping incompatible voice frame on SIP/2000-00000004 of format ulaw since our native format has changed to 0x80002 (gsm|h263)


it is using a codec that was not agreed in the initial codec negotiation.

You could try telling Asterisk to allow ulaw

There are no errors in your log extract. NOTICE means a normally occurring event that might be of interest.