Registration integration with Profile Builder Pro, is it possible? Please help

Just started getting a hang of the plugin.

So, I understand the procedures of member registration is:
1. select membership level on: /memberships
2. register @ /register
3. pay the bill @ /register/?membership_id=level_id

Well, I am trying to replace the step 2 with other registration form (by Profile Builder Pro). I am getting this message:

Fatal error: Uncaught exception 'Exception' with message 'Invalid Membership Relationship' in /home/xgxhosti/public_html/ Stack trace: #0 /home/xgxhosti/public_html/ MS_Model_Event::save_event('signed_up', Object(MS_Model_Relationship)) #1 /home/xgxhosti/public_html/ MS_Model_Relationship::_create_ms_relationship('1118/?autologin...', NULL, '', 0) #2 /home/xgxhosti/public_html/ MS_Model_Relationship::create_ms_relationship('1118/?autologin...', NULL, '', 0) #3 [internal function]: MS_Controller_Frontend->payment_table('[ms-note type="...') #4 /home/xgxhosti/public_html/ call_user_func_array(Array, A in /home/xgxhosti/public_html/ on line 501.

I understand this is caused by the communication between PBP & PC. PC doesn't know which member is created by PBP. Any idea how to make it happen?

Bad Breaks Communications