Error trying to create a sub domain

Hello

I am running the current version of Sentora under CentOS Version 6.  I have a lot of messages in google search engine and some of the messages here they are confusing trying to fix the issue with the error message when creating a new sub domain Your Domain name is not valid. Please enter a valid Domain Name: i.e. 'domain.com'.

Can someone please help me with trying to correct this issue?

Thanks