It seems like that is translator issue which caused this link generated wrongly.
COM_EASYDISCUSS_TOOLBAR_NEW_USERS_REGISTRATION=""_QQ_"Si eres nuevo, por favor <a href="_QQ_"_QQ_"_QQ_"%1s"_QQ_"_QQ_"_QQ_"> registrate para una cuenta </a>"_QQ_""
This is the correct translation string which I already help you corrected this from
/httpdocs/language/es-ES/es-ES.com_easydiscuss.ini
COM_EASYDISCUSS_TOOLBAR_NEW_USERS_REGISTRATION="Si eres nuevo, por favor <a href="_QQ_"%1s"_QQ_"> registrate para una cuenta </a>"
It should work fine now.