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Why does my sugar paste stretch and become un-usable when I cover a cake that has a butterceam coating on itneven tho the cake has been in the fridge

Hello elizabeth_sneddon

Is this a recent thing or does it happen all the time? Are you using the same consistency buttercream for filling and crumb coating? I don’t use buttercream very often but I have noticed that the consistency for crumbcoating has to be stiffer than that for filling. Use more icing sugar for the crumb coat buttercream so it sets up harder.
Paul has a tutorial on how to give more structure to butter cream here:
http://www.cakeflix.com/using-buttercream-giving-buttercream-more-structure
I make a crusting buttercream with melted white chocolate as follows:
250g butter, 500g icing sugar combined until until light and fluffy
Add 100g cool, not cold melted white chocolate and combine until fully incorporated
You can also mix meringue powder into buttercream to help it crust, this is just one recipe, there are many more
http://www.ehow.co.uk/how_5602780_add-powder-buttercream-frosting-strength.html
Some people use half butter half shortening (trex) to make a more stable buttercream. I haven’t ever done this so can’t vouch for taste but have read it tastes good and holds well.

Another reason could be that you are icing the cake too quickly when removing it from the fridge. As it comes to room temperature it sweats and makes the icing wet. Perhaps leave it to come to room temp for half an hour to let any dew dry up. Helps also to run a fan on the cake to ventilate it while covering.
Hopefully other members will help out with tips.

If the weather is particularly warm where you are, butter cream will become soft quickly. Some of the above ideas should help stabilise it.

Thank you for your help….I will run to the supermarket and get white chocolate will keep you posted on the results