Er. What?

I have chosen to opt out of future updates but thought that meant I kept my Splat? I can now not save and am running in demo mode.
Over the years I have spent a small fortune on Cakewalk.
 
What is this rubbish? I have a client in the studio today and cannot work.

I have never experienced this (not updated CCC in eons), but if launching from the CCC does not work, I would first attempt a system restore and see if that does anything.
 
When you get it resolved, I highly recommend an image of your C: drive (I use Macrium Reflect Free). At least in the future that will give a restore option not dependent on Windows.
 
I totally feel for you. Definitely not the best PR with clients in house.

If you go here, it will tell you when your membership expired.  I believe you would need to install the latest version that was released before the date shown.  Can it be assumed that you have made at least 12 consecutive monthly payments or at least a one time payment.

https://www.cakewalk.com/My-Account/Membership

not much info to go by here.
Did you update recently ? Did the update work but now doesn't ?
did you pay for a years worth ?
 
These issue get resolved faster when in the correct part of the forum as well.
http://forum.cakewalk.com/Cakewalk-Store-f79.aspx

Well that was embarrassing. Thanks Cakewalk.