Hi,
Basically, AI works by looking at the changes done to the system during install. This is done by taking two snapshots and comparing them.
By any chance, if the dll was already there in the source machine, install would not install it and AI will not be aware that the file is needed.
If you know the location of the file, you can add it manually to AI (using AI Builder) and re-build the packge. Could you try that?
Krish