Sometime we have different versions of SQL Server installed on our different machines such as Local Machines have SQL Server 2008. Development, UAT and Production has SQL Server 2005 Or our local machines have SQL Server 2012 and all other machines have SQL Server 2008 R2.
After developing our SSIS Package on local machine which has latest version than other machines. If we want to take these SSIS Packages to our Development machine and make some changes, It will not be possible.
Backward compatibility is not supported for SSIS Package.When you create your SSIS Package/s make sure you have same version on other machines where you need to deploy your packages later.
If you have developed your SSIS Package by using SQL Server 2005. You can always upgrade them to SQL Server 2008 Or If you have developed them by using SQL Server 2008 then you can upgrade them to SQL Server 2012 but not backwards.
Couple of reasons why Backward compatibility can be challenge :
There are features/components those are available in latest version but not in old version. E.g If you have used Cache Transformation in SSIS Package that was created by using SSIS 2008 and want to convert to 2005. Guess What! Cache Transformation is not available in SSIS 2005.
Or if you have used the Script task and C# coding in it by using SSIS 2008, SSIS 2005 only supports VB.Net in Script task.