If the column A is stored as int then is likely the empty values are passed as 0 or null therefore you should modify the condition to account for this.
Something like:
// option 1 if the value is passed as 0
dt_YourTable("ColumnA") <> 0 and dt_YourTable("ColumnB").ToString.ToLower.Equals("order executed")
//option 2 if the value is passed as null
dt_YourTable("ColumnA") isnot Null and dt_YourTable("ColumnB").ToString.ToLower.Equals("order executed")
On a side note, have you considered using Filter Data Table
