The ‘Windows Authentication’ check box is disabled at logon
The windows authentication options allows you to use your Windows credentials to log on to WinMan. In order for it to work you will need to have the correct domain set in System Options and be a member of the Domain Users group on the associated domain.
If the check box is disabled but you have met this criteria then an error validating your credentials with the domain has occurred. This may be because the workstation you are using does not have a trust relationship with the domain. You domain administrator should be able to correct this for you.