upgrade from Wix 3 to Wix Toolset 6, Getting error CreateProcessW failed with return code: 193 when running bootstrapper

[MikeGus2]

Question

upgraded from WixToolset3 to WixToolset 6,

We did the upgrade and have our c# bootstrapper UI project (Uses WixSharp 4) compiling. When we launch the created install exe it does not run. In the log we get this error. It worked fine before the upgrade. Is there anything we need to differently now to get this to run?

[9834:1564][2025-12-11T10:16:34]e000: Error 0x800700c1: CreateProcessW failed with return code: 193
[9834:1564][2025-12-11T10:16:34]e000: Error 0x800700c1: Failed to launch bootstrapper application process: "C:\Users\MICHAE1.GUS\AppData\Local\Temp{684D92D3-6A0D-42A9-8528-639280248801}.ba\Bootstrapper.UI.dll" -burn.ba.apiver 569705357157400576 -burn.ba.pipe BurnPipe.{AC5E4B43-03FE-43B3-99AC-3036B03A6BEB} {8CFBDED5-A4B1-479C-88BB-9E13B5EDEA5C}
[9834:1564][2025-12-11T10:16:34]e000: Error 0x800700c1: Failed to create bootstrapper application process: C:\Users\MICHAE1.GUS\AppData\Local\Temp{684D92D3-6A0D-42A9-8528-639280248801}.ba\Bootstrapper.UI.dll
[9834:1564][2025-12-11T10:16:34]e000: Error 0x800700c1: Failed to start bootstrapper application.

Open Source Maintenance Fee

• I (or an organization I'm a member of) pay the Open Source Maintenance Fee by sponsoring the wixtoolset project because I support the maintainers.

[robmen]

That error code:

winerror.h 0x800700c1
#define ERROR_BAD_EXE_FORMAT
%1 is not a valid Win32 application.

Means you are not building an out of proc BA.

[MikeGus2]

Thank you, this looks like it is the issue for sure.

[MikeGus2]

I have everything in place but I cannot figure out where to set the name of the bootstrapper exe to run. Is this done in a config file? Or in my install builder code where I was creating the ManagedBootstrapperApplication object?

[robmen]

It borrows our name, but WixSharp isn't part of the WiX Toolset. You'll need to ask them how it works.

[MikeGus2]

Ok thank you