Issue message SE361 or SE346

Hello Colleagues,

I´m try to create a  PO wrt PReq, but  I have an Issue when the system arise the message SE361 or SE346, I can not get out of TX: ME21N, using the normal buttons: Back, Finish or Cancel... I have to use the command: /n.

Do anyone have the same issue? or anyone can solve this issue?

Thanks for your prompt hepl.!!