Hello M.G.,
I've successfully tested this update going from 2.1 to 2.1.2 as well as 2.1.1 to 2.1.2. The problem is probably that you have some special release of 2.1, although I don't recall sending you one. The date on the composer.exe file for 2.1 should be 4/23/2007.
Instead of using the Help / Software Update option, please try completing redownloading and installing your copy of Composer from
www.notation.com/redownload.htm
That should work. Please let me know if it doesn't.
After this, you will be able to update from 2.1.2 to 2.1.3, 2.1.4, etc. using the Help / Software Update command.
Sorry the update didn't work for you.
Cheers
-- Mark