My external is a lot of data ! Any other way to work this out and avoid the formatting ?
This should work -- I use Paragon NTFS on several Macs. What exact error are you getting? I have seen a few cases where a copy will fail -- I think it was a spurious duplicate file name but can't remember. It was apparently unique to NTFS and Paragon. However in general Paragon has been reliable.
In some cases the copy failure is unique to Finder. IOW doing the same copy from Terminal will work.
Please state the exact error and we will try to help you out. Also try to determine is it happening in the read phase or write phase. Can it be reproduced to a single folder? E.g, if it errors out on a certain file or folder, if you try to copy just that folder or file does it still happen? If it fails on a specific file, does that file name have both upper and lower case letters, spaces, etc? Is it a long filename?
You can also try to run Disk Utility First Aid on the NTFS volume. That will at least verify whether there's anything wrong with the file system.
Make sure you have upgraded to the latest version of Paragon, which can be done in System Preferences>NTFS>Settings>Check for Updates. The current version is 14.1.187.
As already stated if you need PC/Mac data interchange, exFAT is probably better. If it is Mac only then HFS+ is better.
However you already have the data on these drives and you already have Paragon NTFS, so it really should work.