Hi,
If you referring to SAP 64 Bit client, then note:
1. The Add-On solution Target Platform should be x64.
2. The DLLs(SAPbobsCOM, SAPbouiCOM, B1Wizardbase, Any Customized DLL) that you are using should reference 64 Bit.
3. Also the Installer's Target Platform should be x64.
Hope it helps.
Thanks & Regards
Ankit Chauhan