553 Could not create file

Please forgive me if this is a stupid question .... but I'm more of a Windows guy than Linux.

 

Trying to get FTP to work and having trouble with permissions, I think. 

 

The user is userx.  It is in the userx group as well as the root group.  I even set root as the primary group for userx.

 

I can connect fine, but when I try to transfer a file I get "553 Could not create file." 

 

The directory I'm trying to write to (/opt/installs/) is owned by root.  Shouldn't userx be able to write to this directory?  If I open up a terminal window and su userx, I can write fine.  But I can't FTP.

 

Thanks for any help.