Marmotta: Congrats!
I don't know how you communicate verbally, but you could be like me. If I'm going to have a difficult or complex discussion about an issue, I tend to rehearse, think carefully, and even write out an agenda with talking points. This means that when I open my mouth, I sound like a professor lecturing students or dictatorial. Since the lecturing isn't tempered by jokes, smiles, or other non-verbal things that might otherwise put the recipient at ease, it can be off-putting and make me seem overly tough. Once they get to know you a bit better, your staff will understand that you're not *really* lecturing, you just talk that way. They'll even tell their co-workers that "you didn't mean it that way". At least that's what happened with me.
Chummy people can be lousy managers because they have a hard time telling their friends what to do. By not being friends with your co-workers, you were in a good position to manage them but it's like they promoted the square peg. If they are already being annoying (the one day call-off sounds like it), then quietly see if you can communicate with them one-on-one to figure out what their beef is. It could just be that someone popular wanted the job and didn't get it. Someone will likely appreciate you for being straightforward and will return in kind. (Someone else will be suspicious about it, but alas.)
Best Wishes!
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Apologies if I sound judgmental, preachy, dictatorial, offensive or overly rigid. Constructive criticism via PM is welcome.