Modules & VBA :: Click Event To Open A Form And Select Record Corresponding To Value In Unbound Text Box

I have some code for a button on click event to open a form and select the record which corresponds to a value in an unbound text box. The code is:

Private Sub Command25_Click()
On Error GoTo Err_Command25_Click
Dim stDocName As String
Dim stLinkCriteria As String
stDocName = "frmOpenPatientRecord"

[Code] ....

This works fine when I put in a 10 digit NHS number but opens a blank record when I enter a four digit or six character/digit PatientNumber. Both patient number and NHS number are text fields in the underlying table.