Help! Upgraded to Sage 50 2024 and my apps now throw "Unable to cast COM object of type ..."

Ah I forgot to copy over the latest Interop.PeachwServer.dll and recompile like I have to do every year.. nope still fails. Version 31 dated 10/5/2023, looks good.  Downloaded the 2024 SDK to see if anything has changed in the COM interface.. nope, login still looks identical to what I have.

Unhandled Exception: System.InvalidCastException: Unable to cast COM object of type 'System.__ComObject' to interface type 'Interop.PeachwServer.Application'. This operation failed because the QueryInterface call on the COM component for the interface with IID '{E54D916D-FA7A-47A5-A8A1-7EF0AC83818E}' failed due to the following error: No such interface supported (Exception from HRESULT: 0x80004002 (E_NOINTERFACE)).
at MApplication.Main(String[] args)

Im compiling with csc.exe version 4.8.9037.0, referencing the interop dll.

These are just simple apps to pull out invoices to print custom packing slips, Ive been using them for years.

Interop.PeachwServer.Login login = new Interop.PeachwServer.Login();

It throws right here:

peachApp = (Interop.PeachwServer.Application) login.GetApplication("name", "password");

Any other ideas?