You wouldn't normally experience a problem using these SIMMs in the IIcx.
All of them are at least as fast as the specifications require, and you're
not mixing them within a bank (which, technically, is supposed to work,
but often does not).
It sounds more like you have a defective SIMM, probably one of the 120ns.
The self-test does not check the RAM as extensively as our diagnostics
check it. It will try to make sure the lower addresses are good, which
are the SIMMs in bank A, so the operating system will work correctly.
Because it erred with the 120ns SIMMs in bank A, I would suspect those
SIMMs first.
Mouse-freezing can be caused by a variety of things. Basically, mouse
movement is controlled by the operating system, completely aside from all
other system events. All mouse movements are posted to an event queue, as
are almost all other events, and then the events are processed in order of
their occurrence. If a mouse freezes, then the event queue is not being
processed. This means the operating system is hung within an event,
because the operating system is either within an event or getting the next
event.
One such event that causes the system to hang is faulty RAM refreshing or
memory I/O, but the most common is disk I/O. In this case, however, we
think you're dealing with a RAM problem.