That happened to me a while back with Premiere Elements 8.0/8.0.1 installed on a Windows computer.
Resolution came quickly and professionally from the Adobe Chat group (great group).
Please click on the Chat now button of the following link, and your issue should be taken care of in minutes or less by the Adobe Chat professional.
Please let us know the outcome.
ammelgeorge is saying that the Adobe system thinks that the S/N is on two computers already, not failure to activate in the sense that I think you mean?
Could be. However, with mention that the program was installed in 2010, and no mention of it being uninstalled, or reinstalled, lead me to question whether something has changed in the 2010 installation.
Now, if this is a new installation, then I agree that addressing the number of installations and activations woud be the first place to start. With such problems, Adobe Customer Support (not Technical Support) is usually quick.
If this is not that 2010 installation, which has somehow changed, then I would definitely contact Adobe C/S, and still keep that in my mind, if everything else did not work.
The EULA's for different Adobe programs can differ, and even the type of activation can differ, sometimes version to version, plus program to program. In very general and broad terms, most allow installation on 2 personal computers, though not to be used at the same time, plus many have a limit on the number of installations allowed from a downloaded installer file, or physical media. Then, and depending on the type of activation, one is allowed usually two Activations. Depending on what a user encounters, Adobe C/S can reset both the number of times that one can use the installer, or the number of times that a user can Activate the particular software. One good example of resetting the number of Activations is where a HDD crashes and must be replaced, and the user does not have the opportunity to Deactivate a particular program. It depends on the exact program and the exact circumstances.
Good luck to the OP,