KB10793 - Targeting x64 code with Developer Kernel for .NET.

DK9
The DK.NET 9 can be used to compile x64 code. However, there are some limitations:

1. Not all layer formats are supported. Generally formats utilizing external .DLL libraries, such as the ECW format, are not supported because a number of external drivers are still 32 bit.
2. Debugging 64 bits code can cause memory problems with Visual Studio (all available memory consumed by Visual Studio). We are aware of this, but we have no idea why it happens. The same application will run smoothly if outside of Visual Studio. Therefore, we recommend debugging a DK.NET application in forced x86 (32 bit mode) then target x64 (or any processor) only for deployment.

DK10
The DK.NET 10 can be used to compile x64 code. The only significant limitation is lack of support for the MSJET database, because MSJET is not supported on the 64-bits platform at all.