Exception "Object must implement IConvertible" for multiple-field DataKeyNames in a GridView

[dan]

Hi,

I've been using a GridView for some time but this is the first time I need
to delete a row in the grid whose primary key consists of 2 fields (table
columns). I have a table with primary key set to c1,c2 where c1 is a
uniqueidentifie r and c2 is int.

The DataKeyNames in the gridview is defined as follows:
DataKeyNames="c 1,c2".

I have a ObjectDataSourc e defined with following delete params:
<DeleteParamete rs>
<asp:Paramete r Name="c1", Type="String" />
<asp:Paramete r Name="c2" Type="Inte32" />
<DeleteParamete rs>

The ods is mapped to a bll's method Delete(string, int). Unfortunately the
method never gets called.

I attached RowDeleting event handler to the gridview to see the content of
GridViewDeleteA rgs.Keys. The dictionary looks fine there, including key
names and values.
Partial stack dump of the exception that I get afterwards:

[InvalidCastExce ption: Object must implement IConvertible.]
System.Convert. ChangeType(Obje ct value, TypeCode typeCode,
IFormatProvider provider) +2561730
System.Web.UI.W ebControls.Para meter.GetValue( Object value, String
defaultValue, TypeCode type, Boolean convertEmptyStr ingToNull, Boolean
ignoreNullableT ypeChanges) +264
System.Web.UI.W ebControls.Obje ctDataSourceVie w.MergeDictiona ries(ParameterC ollection
reference, IDictionary source, IDictionary destination, String
parameterNameFo rmatString) +439
System.Web.UI.W ebControls.Obje ctDataSourceVie w.ExecuteDelete (IDictionary
keys, IDictionary oldValues) +846
System.Web.UI.D ataSourceView.D elete(IDictiona ry keys, IDictionary
oldValues, DataSourceViewO perationCallbac k callback) +75
[...]

Could someone please let me know how to troubleshoot this?
Thanks,