Adding recurring event on calendar using sharepoint webservice

Question

I'm using the SharePoint webservice to add a calendar event through a vb.net winform, which by itself works fine, but when I try to add a recurring event I get an exception of type "Microsoft.SharePoint.SoapServer.SoapServerException". I'm using the webservice specifically to avoid using the sharepoint component, so I don't think I can get anything useful from the exception.

Here is the code I'm using to build the xml string, which is then submitted with UpdateListItems:

sBatch.Append("") sBatch.Append("" & Title & "")

    If FullDay Then
        sBatch.Append("<Field Name='EventDate'>" & AddToDate.ToString("yyyy-MM-dd") & "</Field>")
        sBatch.Append("<Field Name='EndDate'>" & AddToDate.ToString("yyyy-MM-dd") & "</Field>")
        sBatch.Append("<Field Name='fAllDayEvent'>1</Field>")
    Else
        sBatch.Append("<Field Name='EventDate'>" & AddToDate.ToString("yyyy-MM-ddTHH:mm:ssZ") & "</Field>")
        sBatch.Append("<Field Name='EndDate'>" & AddToDate.AddMinutes(LengthInMinutes).ToString("yyyy-MM-ddTHH:mm:ssZ") & "</Field>")
        sBatch.Append("<Field Name='fAllDayEvent'>0</Field>")
    End If

    sBatch.Append("<Field Name='fRecurrence'>-1</Field>")
    sBatch.Append("<Field Name='EventType'>1</Field>")
    sBatch.Append("<Field name='RecurrenceData'><recurrence><rule><firstDayOfWeek>su</firstDayOfWeek><repeat><weekly th='TRUE' weekFrequency='3' /></repeat></rule></recurrence></Field>")

    sBatch.Append("<Field Name='Description'>" & Description & "</Field>")
    sBatch.Append("</Method>")

The part that I believe is causing the problem is the RecurrenceData field, which I can't seem to find much information on, mostly just examples (which is how I cobbled together the above). Can anyone point me to a resource that enumerates all the valid values for that field or point out what might be wrong in my current string?