I get the error on the same line as you do but when I add Option Explicit, then goto Debug>Compile... I get the same error 3 times here.
Option Explicit

Private Sub cbxTypeEncounter_Change()

    With Me
        Select Case .cbxTypeEncounter.Value
            Case "OH Medicals": .cbxReasonEncounter.List = LookupLists.Range("OHMedicals").Value
            Case "Primary Health Care": .cbxReasonEncounter.List = LookupLists.Range("PHC").Value
            Case "Injury on Duty": .cbxReasonEncounter.List = LookupLists.Range("IOD").Value
            Case "Biokentics": .cbxReasonEncounter.List = LookupLists.Range("Biokentics").Value
        End Select
    End With
End Sub
The reason is you don't have sheet with the code name LookupLists, that's one of the sheets tab name.

Try replacing LookupLists with Worksheets("LookupLists").

I also get errors wherever dteDateSelected, ctrl or FirstRowAdd appear.

PS If want to prevent these types of errors try adding Option Expicit to every module.

You can actually make that happen automatically if you goto Tools>Options... and check Require variable declaration on the Editor tab.