One problem I have seen that has similar symptoms:
If you have SF-17H set to N i.e. you are using the clerk interrupt system, you must have sufficient track headers and track lines allocated in SP-112 to allocate at least one track for each clerk configured (Max Clerks in SP-112) or you won't be able to login in R mode using any method (i-Button, hard clerk, etc.).
Hope this helps ...
Steve
January 2010