UDF behaving oddly
 

The following UDF generates VALUE! errors intermittently and I can't figure
out why. The range argument references another (shared) workbook. It seems
that when this shared workbook is open the function works, when it is not
open, the error is generated. Can this be corrected?

Thanks



Public Function DTD(TIME As Range, CONVTYPE As Integer)

Select Case CONVTYPE

Case Is = 1
minutes = Int(TIME)
seconds = Round((TIME - minutes) * 60, 0)
DTD = TimeSerial(0, minutes, seconds)
Case Is = 2
minutes = Int(TIME)
seconds = (TIME - minutes) / 0.6
DTD = minutes + seconds

End Select

End Function