if you use persistence
Borland.Eco.Persistence.dll
Borland.Eco.Persistence.{specific type}.dll
Pete
And Borland.Eco.Ocl.ParserCore.dll
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Additianally to Peter's and Jan's responses you can have a look at documentation:
Deploying an ECO framework Application
ms-help://borland.bds4/bds4dnettasks/html/eco_deployingecoapplication.htm
Cheers.