If you have are serving Military or MOD Civilian you can log in with your Staff/Service Number; as an alternative to your assigned username. Also your username is usually the first bit of your email address, for example 123muham@armymail.mod.uk or 123muham@royalnavymail.mod.uk.   

For other users, your username is likely to be in the format firstname.surname or it could even be your email address.    You can request your username from the log in page of Defence Gateway - Can't log in - Iv'e forgotten my username

Also please ensure your SyOps is up to date otherwise this will stop you from getting online via DII/MODnet . The SPOC can help you with any issues you have with SyOps or BPS.

If you are still struggling to figure it out or have been locked out please continue to raise a ticket.