Problem is somewhere in SendMail() code of cusmapi, maybe in lnSessionID=THIS.CreateSession(lcUserName,lcPassword), but I don't check it.
I rewrite my code, I first check if the key in registry exists:

on error ... (only return, pnError get error number)
for ii=1 to 2
pnError=0
poMail=CreateObject("cusmapi")
* is key in registry ?
poRegistry = CreateObject("registry")
lcWriteKey = poRegistry.ReadRegistryString()
if not lcWriteKey = Key
* write the key
poRegistry.WriteRegistryString()
endif
if poMail.SendMail()=0
exit
else
... copy MSMAPI32.OCX to system and register
endif
next
if pnError!=0
... error
endif

It's not nice, but it works.
Pavel