If anyone else comes across this problem, the solution seems to be to copy the obj files into the source directory (along side the .pas files referencing them).
>I get the message: 'Unsatisfied forward or external
>declaration: '_deflate'' on line 871 when compiling
>EnCLib.pas using Delphi 6.
>
>My lib path is set to Envision, Envision\Source and
>Envision\D6. What's the problem?