NTFS file system supported although portable hard drive doesn't mount?
CyanogenMod does not support NTFS. You would have to compile your own kernel module for the CM Kernel in order to mount NTFS.



Edit for you comment about the Paragon App:
using an app like that is different then actually mounting it in android. If it doesn't work with your drive, it is an issue with the application, not CM7. 

The app is implementing the NTFS protocol within the application. If it fails to mount, then there is a problem with the application. There are lots of reviews for the app that say "did not work with X", so it seems you are not the only one that has issues.

Your only option is to contact the developer and send them the problem you have, so they can fix it.



In response for your Edit #1 and Edit #2

You will not be able to mount with mount android doesn't have a kernel module that supports NTFS. As I said above, the reason that you can mount it within the app is because the app developer implemented the NTFS protocol in their application. Invalid argument means that the filesystem type you are trying to mount is not supported by mount. No medium found means that it does not see that dev block or cannot access it.

It also sounds like the problem may be that the HDD you are trying to mount requires different drivers to communicate with the HDD controller. Sounds like you are able to get flash drives to work, and that is because they are probably using a "standard" communication, while the HDD could be using something non-standard, or has a different chipset and is not supported by default by the kernel.