Two stage security on private computer

[JAD337]

I recently had to change my password. During that process I set up 2-stage security.

When I sign in on my personal laptop I am asked if I trust this device so I can avoid having to key in a passcode sent by SMS. Obviously I would prefer that. I am then prompted to give my laptop a name of at least 3 characters. Whatever I type in, when I click on "Confirm" I get an error message telling me to use letters, numbers, hyphens or underscores. How do I get past this problem?

[Les-Gibson]

Are you entering a consecutive string with no spaces or other forbidden characters?

[JAD337]

Yes, letters, a hyphen, an underscore and numbers is all I have used. Always more than 3 characters and less than  25.

[Les-Gibson · Accepted solution]

Perhaps the system is seeing your repeated attempts to enter the same name?

If (for example) you clear cookies, then you will be asked to enter a new name and you will not be allowed to repeat any previously used names.

[JAD337]

Possibly, but I  have tried different variations of the name and they've all been rejected in the same way.

I'll try clearing cookies and have another go later today. 

Thanks for your help. 

[JAD337]

Aha! Success! 

I cleared cookies and tried yet another name and it worked!

Again, many thanks for your help.