A few CVS tricks learned today

When I was a normal CVS user (vs. administrator), I always wonder how could
I roll back certain commited changes which I am familiar with in Source
Safe but failed to do it in CVS.

But today, when I right click on a revision (via log window), I saw an
"admin options" which has a menu item named "delete revisions...". Click on
it and confirm, the revision history is gone.

It was all because I am administrator of this CVS Server, otherwise I will
never see it, I guess so.

And something bad happened today, "Log selection" warned as below,
cvs log Create.sql (in directory D:\HRQuizBank\Database\)
cvs [log aborted]: unrecognized operation '\xffffffef' in
/CVS/HRQuizBank/Database/Create.sql,v

I was really familiar with this kind of error, we have lots of them in some
dated cvs repository but no one knows how to handle. Now I tried it myself
and found it was really easy to fix. For example, the first time I saw this
problem today is on revison 1.2, so I delete the changes from 1.1 to 1.2
between two '@'s on the CVS server side file and it was done. The only
problem is I lost the chagnes from 1.1 to 1.2 which I have a local copy.