Need/Iru (..shi) nakerebanarimasen

[chryuop]

Originally Posted by Sashimister

You're using the "right" one. It's mostly, if not entirely, kids that use いけない. If an adult uses it, it just won't sound very good. As for the meaning, they're the same.

That shows how textbooks always lead us student in the wrong way. My textbook for this forms says ーなければ/なくては+ならない and it explains it. In the bottom part of the paragraph it says:
" For the second person (personal note: that is referring to someone I assume) it is more common to use the form ーなければ/なくては+いけない.
A more colloquial form of いけない is だめだ.
Classic form used in literature are ねばならう/なければならう/ねばならない"