It's a very simple problem and should be listed in the foreach command reference. You can not remove member of a collection while enumerating it.

See Re: MisUnderstanding FOR EACH Thread #1329767 Message #1329799

>This seemingly simply process is throwing the error:
>
>

>Collection was modified; enumeration operation might not execute.
>

>
>Here's the code:
>
>

>public void ClearDataStore(string DataViewName)
>{
>    DataViewName = DataViewName.ToString().ToLower().Trim();
>    
>    foreach (DataRow Row in _dsDataStore.Tables[0].Rows)
>    {
>        if (Row["DataViewname"].ToString().ToLower().Trim() == DataViewName)
>        {
>            Row.Delete();
>        }
>    }
>
>    _dsDataStore.Tables[0].AcceptChanges();
>}
>

>
>What's the right way to remove rows from a DataSet????