Rubber bridge: when must honours be declared in order to be scored?
From Law 76 in the American Contract Bridge League laws,


  Honours may be claimed until the next hand has been dealt or the rubber has been completed and scored – whichever comes sooner.


Law 78 also states, with my emphasis on the specific relevant example,


  When it is acknowledged by a majority of the players that a scoring error was made in recording an agreed-up-on result (e.g., failure to enter honors or incorrect computation of score), the error must be corrected if discovered before the net score of the rubber has been agreed to.


Until the next hand is dealt or the rubber complete and scored, honours may be claimed.

The end of a hand is not the same event as the dealing of the hand after it. The rubber cannot be complete until it is know that a side has 100 points below the line, and it is not scored until the sides have both worked out and accepted the net scores from hands played in that rubber.

The referee appears to have made an error if they disallowed scoring honours before the next hand or before the rubber's net score was agreed to. The referee was correct if you or your partner had assented to either dealing the next hand or the complete rubber's net score.