I doubt that condition happened overnight, but in any case if that showed up on my tent I'd be contacting the distributor (Camera Essentials) without hesitation.

http://www.cameraessentials.com/harr...ging_tents.htm

They may have experience with the cause and have resolved it. Check their website and notice the satisfaction guarantee; you could be in line for a new replacement. Did you buy it used or know the conditions of its use? IIRC there was a thread somewhere (possibly on this forum) that talked about the use of insect repellant (DEET I think) that could cause such a condition.