B5Z I feel your pain. It took me more than a dozen tries to get CWM to install. What finally did it for me was I rebooted both the phone and the computer right before I tried and it worked. I ran the tryrunfirst and it failed, then I immediately ran tryrunlast and it worked. This is a completely unrelated topic, but if you read through this thread
[How To] Return to Stock / Fix Bricked Epic - xda-developers you'll see that even the slightest change can make a difference. Change the USB cable, try a different USB port, reboot the phone and PC. I know its not a definitive "do this and it will work" but a lot of the stuff we do on these phones is like that. If at first you don't succeed, change something and try try again.