How to restrict column removal?

*** ActiveX Control Event ***

LPARAMETERS button, shift, x, y

      *     Preciso fazer esta verificacao para impedir que, quando sobrar apenas UMA coluna,

      *     a mesma seja retirada do grid. E' OBRIGATORIO UMA COLUNA

      *

    hitColumn = this.HitTest(X, Y).Column

    If !isnull(hitColumn)

            nVisibleColumns = 0

            nVisibleColumn = -1

            for i = 0 to this.Columns.Count -1

                  this.Columns.Column(i).AllowDrag = .T.

                  if this.Columns.Column(i).Visible

                        nVisibleColumns = nVisibleColumns + 1

                        nVisibleColumn = i

                  endif

            next

          if nVisibleColumn >= 0 and nVisibleColumns=1

                  this.Columns.Column(nVisibleColumn).AllowDrag= .f.

            endif

    EndIf