R help - Dec 2004 - timeSeries to its error

I have a timeSeries that I want to convert to its. When I use as.its()
I get the error:

Error in checkSlotAssignment(object, name, value) : 
        Assignment of an object of class "NULL" is not valid for slot
"units" in an object of class "timeSeries"; is(value,
"character") is
not TRUE

When I constructed the timeSeries object I did not use the units param
in the constructor because I do not know what it does.