error: Data at the root level is invalid. Line 1 Position1

[XML newbie: Urgent pls help!]

I am using VB.Net.
Asset List is a long array of AssetIds. I declare it as:

Dim AssetList(0) As Long
AssetList(0) = 47288

Now, I pass an array of AssetIDs as long from here into the following line:

doc.LoadXml(EDP.ExportPositions(g_SessionID, cmbStartDateandTime.Text,
cmbEndDateandTime.Text, AssetList).ToString) as per the
following function

Public Function ExportPositions(ByVal SessionID As String, ByVal
StartDateTime As Date, ByVal EndDateTime As Date,
<System.Xml.Serialization.XmlArrayItemAttribute("A ssetID",
IsNullable:=false)> ByVal AssetList() As Long) As Position()
When I run the program, I get the error: Data at the root level is invalid.
Line 1 Position1

Pls help. I've nearly smashed my head against the wall trying to figure
this out.