return to my primary model

Hi, i new using workflows and i have a problem, i have my primary model and secondary model, the situation is that i put a buttom "back" beacuse i have return to my primary model y and just put an other linked model to back, but it appears this ErrorMessage = "you cannot perform an array function on a null object" 

i just want that

 back to 

where the primary model had a linked model eSAS Solicitud (first form)

model secondary

i hope that you can help me and sorry for my english , and thanks