Fatal error in two task server.

Hi Gurus,

	I'm seing in my alert log an erro which says
	FATAL ERROR IN TWO-TASK SERVER: error = 12571.
	I can make out from the dump file that this is the error from 
	a session opened from a vb6 program running an insert statement.
	In the process state info i can see one different message 
	<last wait for 'SQL*Net break/reset to client' seq=154
	wait_time=-2
	driver id=(no.), break?=1, =0>
	
	What i can make out from this message is some network timeout has
	occured in the session. But i've noticed the error = 12571 in my  
	alert log many times.
	Can someone enlighten me of the error and the reasons behind that?