.Net Build Error in Final Builder

Question

My project is using an Interface to connect some optional code to my main application. It builds and runs fine during development but when I build it on my build machine I get Errors like the one below.

ERROR BC30456 in C:\calc{list} Build{Pro}\Trunk\plugin Constant Contact\InfusionLogic.CC\calcListCCListColSWB.vb(94,0) : 'IconCol' is not a member of 'InfusionLogic.INTF.IApp'.

Does anyone have any ideas why the interface would work on my development machine but not on the build machine?

Thanks Bob