what your trying to do really doesn't need a sub routine.
from your original page, change this code:
varPostcode=Left((rsUsers.Fields.Item("Postcode").Value),2) 'geeft linkse 2 getallen
varBTWnr=(rsUsers.Fields.Item("BTWnummer").Value)
Call OddEvenNumber(varPostcode)
Sub OddEvenNumber(iNumber)
If iNumber MOD 2 = 0 Or varBTWnr > "0" Then
Response.write ("IBAN : BE02 9793 3516 7640")
Else
Response.write ("IBAN : BE11 9730 2045 8748")
End If
End Sub
to:
varPostcode=Left((rsUsers.Fields.Item("Postcode").Value),2) 'geeft linkse 2 getallen
varBTWnr=(rsUsers.Fields.Item("BTWnummer").Value)
If varPostcode MOD 2 = 0 Or varBTWnr > "0" Then
MailBody = MailBody & "IBAN : BE02 9793 3516 7640"
Else
MailBody = MailBody & "IBAN : BE11 9730 2045 8748"
End If
you're over complicating it by using the sub routine.