RSView32 v6.40.03 was originally released with RSLinx Classic v2.40.01. While this was the latest version of RSLinx Classic available at the time of its release, it would not necessarily mean that RSView32 v6.40 will not work with any other versions of RSLinx Classic. Many, if not all, versions of RSLinx Classic will show as having no known compatability issues with RSView32 v6.40 specifically. That does not mean that they will all work with it, but just that they have not tested all combinations, and for those they have tested, they have not found any issues.
If you do not already have a suitable copy, then RSLinx Classic v2.43.01 is the oldest available for download from the Product Compatibility and Download Center (PCDC)...
https://compatibility.rockwellautom...umb=112&refSoft=1&toggleState=&versions=51543
Click on "Select Files" and you can then select whichever version you wish.
I would be fairly confident that RSLinx Classic v2.43 should work with RSView32 v6.40.
Regards,
George