You can't use Controls with different versions as all our controls, no matter if they are in the Navigation or Scheduler .dlls depend on Telerik.Windows.Controls.dll
which contains some base classes. And you can't have 2 different versions of this dll in the same application.
It is advisable to use the latest binaries as they contain improvements and bugfixes. You can try to use RadScheduler with the latest release. We have made some changes and enhancements to RadScheduler but hopefully it won't be that hard to make it work.
the Telerik team