Nothing. Nothing wrong at all. Even though these men watched Daniel very carefully, they could not find any fault to complain about to the king. God was helping Daniel to avoid doing bad things, because Daniel prayed to Him a lot.
Compare Yourself to Daniel
Have you been late for school?
never
it has happened
sometimes
often
Have you been unjust because somebody promised you something for it?
never
it has happened
sometimes
often
Have you tried to persuade somebody to do something forbidden?
never
it has happened
sometimes
often
Have you worked sloppily?
never
it has happened
sometimes
often
Have you shouted at somebody about something that was not his fault?
never
it has happened
sometimes
often
Have you taken more of something so that there was less left for others?
never
it has happened
sometimes
often
Have you lied in order to look better at something?
never
it has happened
sometimes
often
Have you treated or talked about girls indecently?
never
it has happened
sometimes
often
Have you badmouthed someone?
never
it has happened
sometimes
often
Have you put off unpleasant tasks?
never
it has happened
sometimes
often
If you learnt that you were not doing so well as Daniel, go on reading. You’ll find out what to do about it.