Sorry read your post quickly.
There is a very good chance the issue is your adapter. VGA is never recommended. Also are you sure you downloaded the correct driver?
After the last couple of days I memorized the driver number as well as my El Capitan build number. I have also accessed the kexts to double-check that the web driver is checking for my OS build number (and accessed my SystemVerson.plist to confirm that it is reporting accurately). I am certain. =)
With regard to the cable, it does not seem to make sense that whatever given cable would have any bearing on whether or not the Web Driver control panel reports the driver as compatible with my Operating System.
In any event, according to information found elsewhere, it appears that nvidia web drivers do not properly install unless nvidia drivers are disabled beforehand (using the command in terminal: sudo nvram boot-args="nv_disable=1" ).
Seeing as it was in alignment with your suggested course, and for the sake of chasing my tail (I've little better to do), I went ahead and...
- uninstalled the nvidia web driver,
- used the above command to use the boot argument nv_disable=1,
- rebooted,
- reinstalled web driver 346.03.15f07,
- rebooted again.
Result was identical to the previous situation: web driver complains it is incompatible with my operating system, and the nvidia driver is not selectable instead of OSX Default Drivers.
Additional sources elsewhere indicated that I should follow up that procedure by running another command in terminal to re-enable nvidia drivers: sudo nvram boot-args="nvda_drv=1" So I did that and rebooted. Still no change. Control panel still complains web driver is not compatible with my operating system. No updates are available. No option to switch to the nvidia drivers.
It's all very confusing, because everything seems like it should be in order.
Edit: Another point of clarity. The driver package installs happily, without complaining of a wrong OS (other packages such as 346.03.15f06 immediately complain about wrong OS before installing). It only complains about a wrong OS after it has successfully installed.