I already have seen earlier, that the changeable sender code is not really mature and have already found myself some errors. Basically, if you got an email into the box, that does have an address, which is not defined in the settings, unpredictable things may happen. I am pretty sure, you see an address, which may be a variant of the ones you have in the settings, but is not matching the address as you have entered it in the settings. May you please check, if my suspicion is right? The code does a exact lookup of the addres to be used, so if Domino has sent it to your mailbox as a legal variant of your address, this code will not find it. Unfortunately, there is more of such "magic" inside the code. I hope to find as much as possible before the next release.
If you replace the section with the following code, it will use the very first address in your list instead of throwing an error:
' Which eMail Address To Use
Dim eMailAddressNo As Integer
On Error Resume Next ' As the selected address is not checked for correct value, we may
' not be able to find the correct address
' as a workaround we use the topmost address
' defined in the settings
eMailAddressNo = ArrayGetIndex(colorProfile.MailboxReplyTo,note.SelectFrom(0))
On Error GoTo 0
BTW: Still waiting for IBM for legality of distributing some of their code to make it available again ........