There are few things to note generally about upgrading software versions. Often, it is not the only thing being changed. Sometimes, you are also changing platforms, e.g. from AIX to Linux, this requires migrating (not just copying) the data as well. Also, organisations frequently use the opportunity to introduce/enforce corporate standards, such as standard Autoexecs, autocall macros. These are usually the main cause of coding changes, as SAS (at the code level) is pretty good at maintaining backwards compatability. Applications that are built with code generators, such as SAS EG or SAS DI Studio, have the additional complication that a new version may generate different code, or won't recreate specific customisations. One example that I've encountered in converting from EG4.3 to EG5.1 is code that had been generated as: /* SUM_of_volume */ (SUM(t1.SUM_of_volume)) AS SUM_of_volume became: /* _calculation */ (SUM(t1.SUM_of_volume)) AS SUM_of_SUM_of_volume without modifying the node anew. Needless to say, later steps failed with missing variable errors. In many ways the greatest effort in upgrading versions is in testing your applications. As others have advised, a careful staged approach with both versions running in parallel is safest.
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