My boss called him over to tell him about a mistake he made.
My boss asked to speak with him about an error in his work.
どちらも「上司は彼を呼んでミスがあると言った。」という言い方です。
1) My boss called him over to tell him about a mistake he made.
a mistake を使った言い方。
2) My boss asked to speak with him about an error in his work.
error を使うなら、an error in his work などと言えるかと思います。
ご参考になれば幸いです！
日本 
