I'm getting TypeError: Cannot set property 'next' of undefined

on the following input..

st=>start: Create New Multisite Site
e=>end

op1=>operation: Check if URL has activation ID

sub1=>subroutine: Create Activation ID
sub2=>subroutine: Create User
sub3=>subroutine: Create Domain
sub4=>subroutine: Create Subscription
sub5=>subroutine: Assign Referal

cond=>condition: Yes or No?:
cond2=>condition: User Exists?:

io=>inputoutput: Save activation_id in plugin
io2=inputoutput: Get User

st->op1->cond
cond(yes)->io->e
cond(no)->sub1(right)->cond2
cond2(no)->sub2(right)->io2
cond2(yes)->io2->sub3->sub4->sub5

particularly sticking io2 in the last line breaks things

any idea why?