にも～ない・〜に〜ない: the difference
にも～ないN1
Meaning
Cannot... even if one wants or tries, Would like but cannot, Wants or tries but cannot
Past papers
Tested once in past papers
Example
亡き妻の笑顔は忘れようにも忘れられない。
I cannot forget the smile of my late wife, even if I try to.
〜に〜ないN1
Meaning
Cannot even...if wants, Would like to...but cannot, Wants to...but cannot
Past papers
Tested once in past papers
Example
親友から土下座をしながら頼まれては、断るに断れません。
When my best friend begs me on his knees, I just can't say no.
How to tell them apart
「（よう）にも〜ない」: stuck because of outside conditions, such as a snowstorm or a dead phone.
「〜に〜ない」: stuck because of inner conflict, face or social ties, such as wanting to refuse a kind offer but feeling unable to.