Presumably "establishment" is a user profile field? And its type is drop-down menu?
Can you simplify the problem so that you're only trying to upload one record in the CSV file, it might help you spot the problem. Maybe if you copy and paste the value from the user profile field's Menu options (one per line) list into the CSV field to ensure it matches.
It sounds like you've checked the basics but presumably the problem is something like: if I have a user profile field with two values:
And I have a CSV file:
And I upload these:
Three CSV records get the "Invalid user field" error: 1) lower case 'a' in academy, 2) '1' not 'l', and 3) two spaces in between words.