Setting Fields Based on Checkbox Click

SOLVED

Hello everyone, I'm trying to populate 3 UDFs based off a button click to approve a Receipt of Goods.  Here is the UI script I have linked to the button

'Triggered to write the date/time/name to receiver UDFs
approved=PO_ReceiptOfGoodsHeader_bus_UDF_RECEIVER_APPROVED
sDate=""
sTime=""
newDate=""

sDate = FormatDateTime(Date, vbShortDate)
sTime = FormatDateTime(Time, vbShortTime)
retVal=oSession.FormatDate(sDate, newDate, "%M/%D/%Y")
newDate=oSession.GetFormattedDate(CStr(newDate))

If approved="Y" Then
retVal=PO_ReceiptOfGoodsHeader_bus.SetValue("UDF_RECEIVER_DATE$",newDate)
retVal=PO_ReceiptOfGoodsHeader_bus.SetValue("UDF_RECEIVER_TIME$",sTime)
retVal=PO_ReceiptOfGoodsHeader_bus.SetValue("UDF_RECEIVER_NAME$", oSession.UserCode)
End If

However, when I click the button I get the following errors:

OLE Error Number: 424

Description: Object required: 'oSession'

Script Line 34 which refers to retVal=oSession.FormatDate(sDate, newDate, "%M/%D/%Y")

Any idea what I'm doing wrong?

Thanks in advance for any and all help!