Hi Guido, I'm probably not answering your question, but have you tried
aliasing USERS in your subselects to make completely certain there is no
ambiguity between the various references to USERS? Or even better, replace
your code with

select URID,
URUSER,
USID,
USLASTNAME,
USFIRSTNAME,
URMIN,
URMAX,
URCOMPUTERNAME,
URREPLUSER
from USERS_REPLICATION
left outer join USERS on USERS.USLOGINNAME=USERS_REPLICATION.URUSER
order by URMIN

HTH,
Set