You state the problem in your comment, the number of columns is based on the length of the first line of the file, the second line is longer than the first and therefore there are not enough columns.
I have not tried this out and it might need a tweak but here is a rough fix;
string items = line.Trim().Split(' ');
if (dt.Columns.Count < items.Length)
for (int i = dt.Columns.Count; dt.Columns.Count <> items.Length; i++)
dt.Columns.Add(new DataColumn("Column" + i, typeof(string)));