You almost certainly don't have permission to write to the folder that contains the image file. You'll need to use Windows Explorer to change the permissions to give your user write access to that folder.
As Hal says- "don't have permission"
- In your scenario 1- It is Lightroom that cannot create (and save) the 'copy' that it wants to send out to NIK.
- In scenario 2- You cannot 'Save' or write to the folder, or 'overwrite' the original file.
Hi Hal and wobertc, thank´s for your answers. The problem is that I am the only user on my computer and I´m administrator. I can´t really give me more authorisation ?
Being the only user and admin doesn't mean by default you have read/write permission on all your folders and files. You need to check.
Ok, how do I check this in Windows 10 ? Do you mean that the check box for write protection should be empty in the folders that contains my photos and also in the Lightroom folders ?
To check permissions in Windows (10):
Open FIle Explorer and navigate to the folders to check
Right-click on one folder and choose [Properties] from the drop menu
Select the Security Tab.
Click to highlight one item in the panel [Group or user names: ]
Look in the Permissions box below to check.
You should need "Full Control" checked 'on' for three user names: SYSTEM, Your Name, and Administrators.
Repeat the check for each folder you intend to use with Lightroom.
As Bob says, permissions can change, including, but not limited to, moving files from one HDD to another, OS upgrades, and corrupt user profiles. Search the internet for "Windows 10 Permissions problem" and you'll see many issues. Be careful about diving in and following advice unless you are sure of your problem, and the solution is verified. Too many people suggest "Batch" permission changes, including across the system files, which is usually a very bad idea. Focus on picture folders, and you should be ok.
If you can rule out HDD transfers, OS upgrades and/or transfer etc., then maybe a corrupt user profile. Annoying, but a reality on occasions.
Please post back the resolution here to help others.
Thank you everyone for your suggestions. I´ll come back when I have tried the things you suggested. I´ll post back the solution if I find the correct one.
Problem solved. You have to open Lightroom as administrator. Right click on Lightroom and choose "Run as administrator".