Hydrolic lock for clutch?

locks

#1

i just replaced the clutch in a 94 mitsubishi 3000GT. i was driving it around and everything was normal for about 10 min. then i noticed the clutch pedal was getting harder to push down. soon it got so bad i couldnt push the pedal down to activate the clutch. i got a friend to press the pedal while i bleed the slave. the clutch then worked fine for a little but within a few minutes i started having the same problem. i just replaced a hydrolic dampener for the clutch and the slave plus hydrolic lines. the master is only 4 months old. what could be causing this problem? and how can i fix it.