A subordinate refuses an assignment

A few years ago I managed a larger IT staff than I presently do.  We held regular staff management meetings to facilitate communication among ourselves.  In one of these meetings I tried to delegate an assignment to a junior staffer that would have helped the entire department keep on top of things better.  He refused the assignment.

Here’s a little more background:  The technician had been with the company a few years longer than me and was exceptional at providing great desk side support.  He had an amazing work ethic that brought him onsite typically by 5am and sometimes earlier.  Because he was so responsive to the employees I allowed him to set his own hours.

In other words, he accomplished more before noon than most of the tech support staff could get done in a day.  Because of this he would leave by 2:30 most every afternoon.  I and a couple of other technicians covered the workload the remainder of the day.  However, sometimes we were not quite sure of the status on some open tasks that day.

The assignment I tried to give him was to download and install a piece of helpdesk management software.  I asked him to check it out, feed it for a few days and determine if it would work for our organization.  “Absolutely not!” he exploded when I gave him the assignment.  He then gave a few off the cuff reasons why it was not a good idea.

Here is the dilemma:  This was a subordinate refusing an assignment from his direct manager in front of the rest of the IT staff.  I was a relatively new manager and was still trying to establish a good team atmosphere.  We worked in a high pressure and somewhat stressful environment with several dozen support requests each day among four of us.

Before I tell you what I did in this situation I would like your ideas.  What do you think I should have done?

Update: Thank you for all the comments.  The rest of the story is in a new post, "When management is wrong."