What version of SSIS are you using?
I sympathise. Can you confirm that you have got to the point where:
a) Package 1 works.
b) Take a copy of package 1 (as per my first post) and save as package 2. No other changes are made to package 2.
c) Package 2 fails.
If so, this is surely a meta-data issue. Other than firing up an XML editor or text -file differencer and putting your Sherlock Holmes hat on, I'm not sure what to do next. Actually, considering upgrading to 2012 would be good - there seem to be fewer problems like this with it 🙂
If you haven't even tried to resolve your issue, please don't expect the hard-working volunteers here to waste their time providing links to answers which you could easily have found yourself.