grammatical error

What error would that be? It's awkward, but it is not incorrect.

Old fashioned:
So hoarse he was that he could not make the speech.

So hoarse was he that he could not make the speech.

Poetic:
So hoarse was he that the speech he could not make.

More modern:
He was so hoarse that he could not make the speech.

The first three are not "incorrect".

Explain the error

He was so hoarse that he could not make the speech.