Cannot import row because: Username in use

Hi I am trying to update only certain fields in my CB user database and have followed the CB Operations Guide and Forum posts on Importing Users.
Steps:

1. Exported DB from site using CB export
2. Deleted the columns that are not to be changed
3. Left ID, Name, Username, Email + the fields that are manually cleared to prepare for renewals
4. When I import the CSV with settings Override Existing Entries with Records Matching IDs and Ignore Emails for New Entries, I get the error Cannot import row 1 etc because: Username in use. It impacts every row I am trying to import.

I should add that none of these users are logged in to the site or backend.
Pls help! Thanks.

It sounds like the usernames you've set for those import rows match existing usernames on the site. Seams to be working fine in my tests. Maybe an encoding problem altered the usernames when editing the CSV? Note since you're just doing this to update existing users you only need the id column and whatever columns you're trying to change.

Ys, I did try to include only the ID columns but it prompted me that username, name or email was missing! Inserting only columns for either username, name or email still prompted same message.
Yesterday: I did a CSV export, saved as an Excel to make the changes and then saved back as CSV. Would that have caused encoding issues?
Today, I exported as CSV, updated relevant fields and saved as CSV then tried to import - see image 1 for error 
2nd test, deleted username and then tried to import - see image 2 for error
3rd test, deleted username and email and tried to import - see image 3 for error
4th test, deleted name, username and email only User ID - see image 4 for error

What is the issue pls?

Ys, I did try to include only the ID columns but it prompted me that username, name or email was missing!

That means it's trying to create new users instead of edit existing.

Yesterday: I did a CSV export, saved as an Excel to make the changes and then saved back as CSV. Would that have caused encoding issues?

Yes. Your issue is probably an encoding one. You need to use the below settings.

1. Character set: UTF-8
2. Separated by Comma
3. Format quoted fields as text
4. " as string delimiter

If these aren't used the raw CSV file won't be saved correctly and won't parse correctly. We provide XML and JSON export/import as well so you might want to consider a different format if you can't get your editor to open it correctly. The above work out of the box with LibreOffice. I do not own MS Excel to test if it opens correctly immediately or if further settings need adjusted.

Thanks but to be clear, the subsequent tests were ALL direct CSV to CSV as explained. Could you advice why these errors would occur with direct export and import?

You mean you edited the CSV files in a text editor? What program are you using to edit the CSV?