This is an issue that you will have to resolve with Adobe. Here is the link to where you can initiate a live chat with an Adobe employee:
Click on the long blue bar, and one of the options will be to do a live chat.
When I follow that link and click the long blue bar, it doesn't even list live chat as a support option for Lightroom, and it tells me that phone support isn't available for that product.
When you see the message- "...need to deactivate...."
Is there a button to [Continue] with the activate?
If I recall correctly- When you continue to activate from this message, then Adobe will de-activate all other registrations you have for Lr.
If you run two copies of Lr, you would then need to re-activate the second copy as well.
No. When it tells me I need to deactivate, it presents me with two options:
1. "Retry activation. I have already deactivated one of my other computers."
2. "Provide a different serial number."
For obvious reasons, both of these are not workable options.
It seems that Adobe has changed the links again. Try the following link, choose Lightroom, then choose Adobe ID and signing in. Then click on the blue bar. The live chat option should be there:
An extract from Victoria Bampton's site-
You can have 2 machines activated at a time. If you try to log in on a 3rd machine, it asks if you want to deactivate the other machines remotely, so you don’t have to remember to deactivate or go through a nightmare phone procedure to unlock it.