No Login Box for FlatOne When myBB installed in subdomain

[FlatOneUser]

I have my primary domain set up as "www" as usual.  It does not have an instance of myBB.  Just plain HTML.

I have 12 subdomains with myBB underneath the primary domain, for example: board1.mydomain.com, board2.mydomain.com, board3.mydomain.com, etc...

The default myBB theme works perfectly in the subdomains.  When I click on "Login", the modal dialog box pops up.

When I install the FlatOne theme in the subdomains, clicking on the "Login" icon does nothing.

If I restore the default myBB theme again, the "Login" icon works perfectly.

Q: Has anyone else had this problem?
Q: Am I in the right place for support?

Thanks in advance!