Staple plunger will not retract

My new Roberts 10-600 stapler failed on the second day of use. I am installing a vapor/ insulation barrier in my garage and using this stapler for the job of attaching the barrier onto the 2X4's. I shot approximately1000 staples and now the plunger that drives the staple into the wood will not retract.. You can manually drive the plunger back into the housing and it will fire one staple and stick again, It has been properly oiled after the initial use and now, the second day it worked for about 15 minutes and failed. Any suggestions?