Hi,
I have got the error :
Error: Server xxx:6400 not found or server may be down (FWM 01003) null while login to Central Management Console
Root cuase : The issue was CMS DB connection becuase of updated tnsnames.ora
As database is oracle , I have updated the tnsnames.ora by adding connection entry to CMS DB.
Then it worked fine.
Regards,
Rohan