You should be linking your register page to the blog where BP is installed.
eg. mydomain.com/register (i’m assuming mydomain.com is the blog where BP is installed)
You can use bp_get_signup_page() to grab the registration URL.
Thanks for the fast reply Ray. I can’t use more than one register page?
You want separate members for each blog?
Is that the reason why you would want a separate registration page?
Yes. I have multiple blogs and each blog needs a separted profile, because each blog has a different contents. Is that possible? Thanks again!
You’d need to configure BP for multi-blog support:
https://codex.buddypress.org/how-to-guides/changing-internal-configuration-settings/
This is where I have a knowledge deficit.
I’ve never had to deploy a WPMU multi-site setup.
Perhaps you can contact andrea_r (https://buddypress.org/developers/andrea_r) as she’s well-versed with WPMU and multi-sites and how it works with BP.
Would this allow for the main site to not be a BuddyPress site but the main WordPress MU domain (www.mydomain.com).
Then when a new blog is created it would be it’s own buddypress private social area, lets say for company XYZ.mydomain.com.
Then employees from XYZ could come to XYZ.mydomain.com and register from there?
This is what I’m trying to do with my requirements I have. If we are looking for the same thing maybe we can help each other and forward the answer to each other when we find it.
Thanks Ray, I will contact Andrea. Rgauny, it’s not the same problem. Sorry.
@rgauny
This isn’t related to marcoslavorato’s problem.
Your issue can be resolved by defining the BP_ROOT_BLOG.
Read this:
https://codex.buddypress.org/how-to-guides/install-buddypress-on-a-secondary-blog/
Main blog would be mydomain.com
Secondary blog with BP enabled would be xyz.mydomain.com.
This would work only if you plan on having one community and not multiple communities.
Great! thanks for the reply….I will try and post back with my findings. But what you are saying is it is totally possible to do currently, out of the box, what i am trying to do?
What i mean is if my root MU install does not have Buddypress (mydomain.com). and I want to be able to create private company social network “subdomains” like xyz.mydomain.com and abc.mydomain.com…..both these sites will be totally isolated as far as their user registration, user interaction/communication , group setup etc…..because xyz doesnt trust or want to be involved with in any way abc?
The advice I gave above for you is not going to work then.
Wait for someone who is more familiar with WPMU and multi-sites to answer your question or you can do what I mentioned to marcoslavorato and bug andrea_r 
Ok Thanks for the help man….I will bug andrea_r LOL
