I have a dataset containing a datatable, and I enumerate all rows in that datatable. When trying to format a column in that row, I run into an exception. (Part of) the code is:

```
For Each dr As DataRow In ds.Tables("records").Rows
    file = dr("timestamp").ToString("yyyyMMdd") & "~.wav"
Next

```

This results in the following error message:

**Conversion from string yyyyMMdd to type Integer is not valid.**
(translated from a Dutch error message to the English equivalent)

dr("timestamp").GetType.FullName results in "System.DateTime", so I don't understand why I run into this exception, as for example **Now.ToString("yyyyMMdd")** results in "20091002", and "Now" is of the same type as dr("timestamp"), "System.DateTime" that is.