I would recommend reviewing the Captiva Capture 7.6 Programming Guide at Scripting Guide -> Profile Scripting -> Procedure -> Creating profile scripts as there are a lot of requirements such as the naming convention, references, target framework, etc. Also another requirement, not sure where it is detailed, is that the name of the document type defined in Captiva Designer and used in the CaptureFlow must have a class name in the Custom.InputAccel.UimScript.dll the same name as the doc type but with a Script appended to the beginning. So if your document type defined in Designer was AutoIndexing, then the name of the class in the dll must be ScritpAutoIndexing. Are you familiar with the sample OOTB processes? The AutoIndexing document type has a profile script that could be used for reference. Or just use the entire OOTB Profile Script as a starting point and then just make modifications to it that way you know it contains all the correct parts necessary for the project.
Hope this helps.