Administrative error means that the court clerk or other official did something incorrectly. Sounds like the clerk closed the case while the trustee was still working on it, and once this problem was caught, the clerk reversed the previous order to allow the work to continue. Hope this perspective helps!
As the others have said; something went wrong.
Clerks file things that they shouldn't sometimes. Or other glitches occur.
I've seen a discharge issued when the second course wasn't filed; this resulted in administratively setting aside the discharge.
While the facts you provide are limited, I can intuit from what is stated that your bankruptcy case was closed, but that someone (perhaps the U.S. Trustee or the Chapter 7 Trustee) has filed a motion to reopen the case and vacate the order of case closure. There could be a large number of reasons for this ranging from the discovery of an asset not previously listed on your schedules that could be administered by the bankruptcy trustee and a precursor to a potential "revocation" of your discharge to something far more innocuous such as an accounting error in the Trustee's first and final Report that wasn't discovered until recently. In any event you, should have a lawyer look on PACER to discover what the issue is for your own peace of mind.
First thing I would do is call your bankruptcy attorney and discuss the error. An administrative error is usually a technical problem that happened either by the Clerk's Office of the Trustee. Perhaps they missed a deadline, forgot to file something, or (and this is very common) the bankrutpcy court clerk's office forgot to mail something out or serve someone notice.
Usually administrative errors do not have an effect on your bankruptcy, your receiving your discharge, or your assets. However, one thing to note is that while your case is open, someone can file an adversary proceeding against you (and even after the case is closed once they move to reopen). In an effort to be overly cautious and protect yourself, you should discuss this error with your attorney.