Modules & VBA :: Unbound Text Box To Update Value Of A Table

So I have this code in an afterupdate event in an unbound text box to update the value of a table if the textbox is updated:

Code:

Private Sub txtCustRepID_AfterUpdate()
'Go to Calls table and find original value for CustRepID
'Fin the Call ID first
Dim CallIDVar As Long
Dim ContactIDVar As Long
Dim CustRepIDOr As String
CallIDVar = Forms![Contacts]![Call Listing Subform].Form![CallID]

[code]...

This code works well when entering numbers in the text box but it returns error 3061; "Too few parameters. Expected 1" when along with the numbers there is a letter in the textbox.The error happens in this part of the code:

Code:
'Accept change and add new value to table
CurrentDb.Execute _
"UPDATE Calls " & _
"SET CustRepID = " & CustRepIDNew & " " & _
"WHERE CallID = " & CallIDVar, dbFailOnError

The underlying table has text as type of data for this field.