Retrospectively creating a branch - howto?

[Simon Brooke]

[apologies if this goes out twice - I tried it on my local server but
that appeared to fail to propagate, probably because my upstream server
doesn't carry the gnu hierarchy]

About a month ago I made a decision to make a major change to one of my
library APIs. The change was one I'd been planning for a long time, and
it will (when it's finished and working) be a good thing, but at
present it doesn't work and my applications won't build on top of it.
Unfortunately I neglected to branch the CVS at the time.

In the meantime a bug has been detected in the 'stable' version and I
need to fix it; and I can foresee that the old stable version is going
to need to be maintained for some time. So I badly need to create a
branch as it was on the 10th April.

What I've done so far is:

-[simon]-> cvs co -D2005-04-10 jacquard
-[simon]-> cd jacquard
-[simon]-> cvs tag -b jacquard-1-10-stable-root
-[simon]-> cvs tag -b jacquard-1-10-stable-branch
-[simon]-> emacs README   # to create an observable change
-[simon]-> ant install dist  # to ensure I can build a working version
-[simon]-> cvs commit -m "start of stable branch"

Unfortunately this fails:
cvs server: cannot commit with sticky date for file `README'
cvs [server aborted]: correct above errors first!

I am concerned not to make a mess of my repository, or damage current
work (tagged jacquard-1-11-0). What must I do to get changes to
jacquard-1-10-stable-branch into the repository?