Thank you, Dell and Don. The issue was resolved by simply installing the 64-bit Oracle Client. It seems obvious after the fact, but this problem was really taxing my brain......
Don, to answer your question, the report was developed using the full version of CR 2013. The C# program then referenced the .rpt file. It uses 3 dlls - CrystalDecisions.CrystalReports.Engine, CrystalDecisions.ReportSource and CrystalDecisions.Shared. I don't remember if those dlls were installed with the product, or given to me by a member if the SAP support group.