Forms :: Locate A Record On Multirecord Form By Using Findfirst Method

I am trying to locate a record on a multirecord form by using Findfirst method. Here is the code.

Dim UA1 As String, UAE1 As String, UA2 As String, UAE2 As String, UA3 As String, UAE3 As String, apost as string, repl as string
apost = "'"
repl = "''"
UA1 = Nz(Forms(ParName).Form.NAME, " ")
UAE1 = Replace(UA1, apost, repl)

[Code] ....

This code sometimes works and sometimes it does not work. The field CNO is a text field of 5 characters but contains the card numbers that is numeric data or nothing.