Access 2000 update

I have been able to use statements like this for "insert", but not update.

UPDATE PC SET digits = (select info_add from info_add_ip)
WHERE (pc.compn = (select info_add from info_add_pc));

the error is: "Operation must use an updatable query"

This part of the statement is what is causing the error:
SET digits = (select info_add from info_add_ip)


I have removed any relationship that could hinder the update.

Any help is appreciated.