ODBC user rights

For the ODBC side of our database, we have 2 users set up, the
administrator and a read-only user. After the last dump and load and
patch upgrade (530), the read-only user does not function any more.
It seems to accept the password but when I try to open a table as that
user, the system responds that I lack authorization. This happens
regardless of the application; Crystal, Excel or Access. The reports
still work when logged in as the administrator user.

My plan is to come in Sunday (have to shutdown the database) and grant
rights to the read-only user again. I am not real confident that will
be successful since I cannot see what might have taken those rights
away. We have done dump and loads before without blowing away grants.

Does anyone have any ideas on how to determine the best course of
action? (Ideas that can prevent an unnecessary Sunday trip are
especially welcome.)