Sorry to hear this, but could you check out this link below first and share as much info as possible?
http://www.reefcentral.com/forums/showthread.php?t=1852463
Beleieve it or not, fragging is also stressful. Stress can also induce these infections expecially after fragging if not performed properly.
After you frag, what do you do to and with the mother colony and the frag?
How many times has this happened?
When was the first time and did it coincide with fragging?
Have the retracted polyps bounced back or do they always perish?
Is this a new system? If not, how mature is it?
Mucho