“Because of he was ill”这句子有错吗？为什么？

当然有错，because 和 because of虽然都表示“因为”的意思，但是他们还是有区别的。
简单的说，because后面跟句子，because of 后面跟名词~~~
这句话可以说 because of his illness或者是because he was ill.

Because he was ill.

有,
because he was ill
because of后不加句子

because of后接名词，不能接句子
这句话应该改成
because he was ill
或because of his illness

有错误because of 后面只能接名词或名词词组
而because 单用的时候才能加句子
可以该成：
Bscause he was ill./Because of his illness.

错,because of 后面只能接名词或名词词组
可以该成
Because he was ill./Because of his illness.