I see a couple of issues.
Why would you update the Reservations_Amount_Owed value in the BeforeUpdate event of same? I would expect it to be updated in an AfterUpdate event for Combo70, Reservations_Number_of_Tickets or Reservations_Ticket_Price, probably a separate procedure called by all three AfterUpdate events.
Second, never, never, never hard-code that 2500 into your program! Create a tblRate, give it a RateCode, start and end dates and a rate. Then pass the date of the reservation to a function that returns the amount owed based on a given date.
Me.Reservations_Amount_Owed = GetRate("Corp", Me.Reservations_Date)
public Sub GetRate(byval RateCode, byval selDate)
dim dbCurr as database
dim rstRate as recordset
dim strSQL as string
strsql = "SELECT Rate from tblRate " _
& "WHERE RateCode = " & RateCode _
& "AND StartDate <= #" & selDate & "# " _
& "AND EndDate >= #" & selDate & "#;"
set dbcurr = currentdb
set rstRate = dbcurr.openrecordset(strsql)
if rstrate.records.count > 0 then
GetRate = rstrate!Rate
GetRate = -1
set rstrate = nothing
set dbcurr = nothing
The Me.Reservations... goes in your form, the GetRate would go in a separate module.