Actually CarMaker should accept win64 DLL, as you can read in the features and functions list, since CarMaker 5.0, at the following link from IPG Automotive website:
Therefore, if the FMU passes the compliance checker and you are able to re-import the FMU in Simulink and everything works fine, this issue comes from the CarMaker side and should be checked with CarMaker.
If not, you maybe missed some steps in CarMaker. Please be aware that this is a 3rd Party Product and our Technical Support team is only providing support for our own products.
In the attachments you find a PDF with some screenshots with the most important steps, where you can see how the Simulink FMUs can be imported into CarMaker.
Beginning with R2020a, you can export your Simulink model as a standalone FMU with Simulink Compiler . When a third-party tool runs the FMU, no MATLAB or Simulink license will be required.
Beginning with R2019a, the ability to export a Simulink model to a tool-coupling FMU is available in Simulink:
Wrap your Simulink model and project files into an FMU that has a co-simulation interface. When a third-party tool runs the FMU, the FMU checks out the required MathWorks® licenses, starts a local MATLAB® session, and runs the model.
In R2018b, a MathWorks®-provided support package: "Tool-Coupling Co-Simulation FMU Export for Simulink support package" is required
While we recommend this to be downloaded through the Add-On Explorer, a link to open it in Add-On Explorer is available on File Exchange:
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