>commercial

IF it is a "shrink wrap" or "download" then it should be your responsibility. You charged them for a product. If you don't fix it and they exercise remorse then you would need to give their money back.

It's just like returning a malfunctioning watch to the store. THe store will either replace it or refund the purchase price.

You should disclaim against loss of data and system problems - those you can find in almost any end user license - but if it's broke - you got to fix it or replace it.