One obvious question is, how does the expression look like when it's added into the filter. using debugger, place a breakpoint on the line where you set the filter and ensure that the filter has proper value. For example is the text in combobox written exactly the same way how the column is named in the data source
When clearing the filter, instead of setting an empty string to the filter, it's recommended to use
BindingSource.RemoveFilter Method (System.Windows.Forms)[
^]
I take it that the idea is to allow user to search with partial text, in other words the text does not need to match the value in the data source in whole. If this is the case you probably should change the equality comparison to LIKE. In other words something like
customer_OrdersBindingSource.Filter = string.Format("{0} LIKE '{1}*'", comboBox1.Text, textBox5.Text);
For more information, see
DataColumn.Expression Property (System.Data)[
^]