I made marshmallow fondant ,double wrapped in plastic wrap then placed in a ziploc bag and stored in the refridgerator as directed. A week later i colored the fondant , rolled it out ( it was beautiful to work with) covered my cake and within a hour it was sweating , sticky and sagging! It eventually firmed up after a couple hours of having a fan blow in it.  

Another time i was covering a wood shoe mold for a boot cake and the same thing happened. by the morning the fondant was sagging and looked like it was dripping on the bottom! Help

I wonder if putting in the fridge affected it somehow. I have never put my mmf in the fridge and not really sure why you would. I just wrap it really well and leave at room temp. :)

I have had fondant get really wet/sticky like that.  I attributed it to the extremely high humidity where I live. 

If it is very humid outside, your fondant will sweat.  Don't use corn syrup (or use less) in your MMF recipes on hot and humid days to minimize sweating.