This happens sometimes with Unix versions of ChemApp/ChemApp light, for instance
- you need a 64-bit version but the distribution archive contains a 32-bit version,
- you need a version that does (or does not) have underscores prepended to the subroutine names, and you need a version that has been compiled exactly the other way.
In most cases, we’ll be able to help you by compiling a custom version for you. Just contact us at firstname.lastname@example.org.