Python: 1961 bytes, score=1207
Here's my submission:
import sys
b='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'.decode('base64').decode('zlib').split(';')
R=raw_input
def G(c):print c;sys.stdout.flush()
def P(w):
if'END'==w:exit()
d=b[len(w)].split(':');p=f=0
for i in range(4):
G(d[0][p]);x=R();r=w==x;w=x;f+=r;p+=p+1+r
if'_'not in x:return
for c in d[p-14]+'zz':
G(c);x=R();r=w==x;w=x;f+=r
if'_'not in x or f>5:break
while 1:P(R())
Scored output:
score is 1207, totalerr is 21603
It's fully deterministic, and pretty well golfed. How this works is left as an exercise to the reader, for the time being.