Find Form And Stlinkcriteria

I have made two forms which I use to find particular records on another form and one works and the other doesn't. I can't figure out why one works and the other doesn't.

The working code is:
Private Sub Project_List_DblClick(Cancel As Integer)
On Error GoTo Err_Project_List_DblClick
Dim stDocName As String
Dim stLinkCriteria As String
stDocName = "Project Details Form"

stLinkCriteria = "[Project No]=" & "'" & Me![Project List] & "'"
DoCmd.OpenForm stDocName, , , stLinkCriteria
DoCmd.Close acForm, "Project List", acSaveNo
Exit_Project_List_DblClick:
Exit Sub
Err_Project_List_DblClick:
MsgBox Err.Description
Resume Exit_Project_List_DblClick

End Sub

[Project No] is the primary key in the Project Details. Also, it's the bound to column in the [Project List] list box.

The non-working code is:
Private Sub Assessment_List_DblClick(Cancel As Integer)
On Error GoTo Err_Assessment_List_DblClick
Dim stDocName As String
Dim stLinkCriteria As String
stDocName = "Site Assessment Details"
stLinkCriteria = "[Assessment ID]=" & "'" & Me![Assessment List] & "'"

DoCmd.OpenForm stDocName, , , stLinkCriteria
DoCmd.Close acForm, "Site Assessment List", acSaveNo
Exit_Assessment_List_DblClick:
Exit Sub
Err_Assessment_List_DblClick:
MsgBox Err.Description
Resume Exit_Assessment_List_DblClick

End Sub

[Assessment ID] is the primary key in the Site Assessment Details and the bound to column in the [Assessment List] list box. One difference between the two is that the Assessment ID is a column of 0" width in the list box of Assessment List and a hidden text box in Assessment Details. Assessment ID is a autonumber field. I've tried to make the column have a width and show the ID on the details form and it hasn't seemed to make any difference.

Any ideas about what the key difference is?

Thanks