cronus.dll (along with VpEnc.dll and VPSoloDec.dll)
is V-Vocal.
It is also an ActiveX library, which means it has to be registered in order to work. If it's not registered, SONAR will not be able to link to it at runtime and a nasty error will be raised when you attempt to invoke V-Vocal.
Registration should take place during installation, but if anything (e.g. insufficient Windows permissions) prevents that from happening you'll need to re-register it manually. I have also seen ActiveX libraries become un-registered after a successful installation, but I do not know why that happens.
To manually register an ActiveX DLL, use the REGSVR32.EXE utility. At the Windows Run prompt (or in a DOS window) invoke REGSVR32 twice, once to un-register the DLL and a second time to register it:
REGSVR32 /U "c:\program files\cakewalk\shared dxi\vvocal\cronus.dll"
REGSVR32 "c:\program files\cakewalk\shared dxi\vvocal\cronus.dll"
If REGSVR32 fails, it will say so and give you an error code that indicates why the registration failed. If you've given the correct path, AND cronus.dll actually exists, the most likely cause of failure is that your Windows profile does not have sufficient rights to modify the HKEY_LOCAL_MACHINE registry hive. The second most-likely reason is that cronus.dll itself is corrupt.
(For many DLLs, the most likely reason for failure to register is a missing dependency. However, all of cronus.dll's external dependencies are standard Windows files so this shouldn't be an issue unless you've got a serious problem such as a mismatched OLEAUT32 or something.)
The other two DLLs are static libraries and do not require registration.