Help with an if/then and displaying a message syntax in a form

[TAM]

The first if statement is working as desired, however I would like to add a message popup that if the user has "yes" in the first field and "n/a" in the next field, they need to select a measurement. Can you help me with the syntax, please?

Private Sub Next_yr_Impact_Change()
Dim Message As String
If Forms![frm_exception_updateModal]![Next_yr_Impact] = "No" Then
Forms![frm_exception_updateModal]![Next_Grid].Value = "n/a"
Forms![frm_exception_updateModal]![GDC_Baseline_Adj].Value = 0
Forms![frm_exception_updateModal]![FP_Baseline].Value = 0
ElseIf Forms![frm_exception_updateModal]![Next_yr_Impact] ="yes" and forms![frm_exception_updatemodal]![Next_Grid].value] = "n/a" Then
Message = "Select Measurement"
End If
End Sub

 

[Micron]

Msgbox "Select Measurement"
If there are other possibilities, like the user may not enter yes, but does enter a grid value (or vice versa), or enter or enter "na" the routine will fail. For more message options, check out the message box function.

PS's: Rarely do you need to reference .value for a form control - it is the default property.
Once your message is dismissed, there is nothing to stop the procedure from running to completion, except error causing code such as this [Next_Grid].value] Note my Exit Sub further down.
Here's a way to type less code

Dim frm as Form
Set frm = "Forms![frm_exception_updateModal]"
If frm.[Next_yr_Impact]...
For larger blocks of code in a post (like what you posted) please use code tags, with the customary indent. Makes it much easier to follow.

Private Sub Next_yr_Impact_Change()
Dim Message As String
Dim frm as Form

Set frm = "Forms![frm_exception_updateModal]"
If frm.[Next_yr_Impact] = "No" Then
  frm.[Next_Grid] = "n/a"
  frm.[GDC_Baseline_Adj]= 0
  frm[FP_Baseline] = 0
ElseIf  frm.[Next_yr_Impact] ="yes" and  frm.[Next_Grid] = "n/a" Then
   msgbox = "Select Measurement"
  Exit Sub
End If

End Sub