Activation Limit is one computer on CS5??

I've read some of the other threads on this subject but none really answers my question. When I bought a new Mac Pro after many years of a G5 and upgraded it to Lion I could not run my ancient copy of the original Adobe Creative Suite (1, I suppose) so bought, at great expense, as you cannot upgrade from CS1, the then new CS5 Design Standard. Works perfectly.

Recently, I had to upgrade my MacBook Air to Lion to avail of iCloud, and of course CS1 won't run on Lion. So I installed my new CS5 suite software on the laptop, via the installion disks. But every time I try to use it on the laptop, a warning panel pops up to say CS5 has already been activated on two computers and I must correct this problem to continue. In other words, I must deactivate the software on one of my other computers.

But I only have two computers.

I gather from threads here that Adobe allow you to run CS5 on two personal computers as long as the software is not running at the same time on both. So I have even tried switching off my Mac Pro, but the problem persists. It's as if Adobe believes I have installed the software on three computers, not two. Has anyone experienced this before, or does anyone have any suggestions? Thanks.