Not a valid Subdomain/FTP username

[DiMora]

Can someone please help? I purchased a new domain, and want to add to my existing host account. When I enter the domain (nutritionaldietplansforwomen.com) and then (nutritionaldietplansforwomen) into the Subdomain/FTP Username I keep getting an error ~ "That is not a valid subdomain/FTP user name". Does anyone know what is going on? I've added domains before and never encountered this problem.
Thanks in advance
DiMora

[DiMora]

Re: Not a valid Subdomain/FTP username

Okay, I got my answer. FTP name to long. Thanks anyway everyone.