"That, is crazy."
"Preparing and submitting his report to the committee for evaluation and possible publication, was one of the most difficult tasks Bill had ever attempted."
In both these sentences you separate the subject from the complement with the comma. That is not correct. You could emphasize the current subject like this:
One task in particular was one of the most difficult that Bill had ever attempted: preparing his report and submitting it to the committee for evaluation and possible publication.
The comma after but is not correct either.