The first thing to check is to make sure you do not enter in the dashes, also, do not copy/paste the number into the field.  This will cause errors.
If the above steps do not work and the error message still shows, this can only mean the product you are trying to activate does not match [...]

Please launch the onOne Software plug-in from Photoshop. Once the plug-in has launched, please choose the deactivate option from either the HELP menu or Photoshop menu inside the plug-in. Please DO NOT choose to remove license.  Removing the license will make your license code completely inactive.  Once you have deactivated from one computer you can [...]

To prevent this error from appearing, please follow these instructions.
Please create (or have your IT department) an exception for the web IP address, name and port below. Once you have done this, please run the installer again.
www.ononesoftware.com
209.162.184.76
standard web  port 80

The steps below will resolve the issue.

Mac users:

Please launch the Activity Monitor (Go to the Mac HD\Applications\Utilities)
Choose “All Processes” in the upper right pull down menu of the Activity Monitor
Locate the process named NalpierondVb, select this process and then click on the Quit button (you may also see NalpeironV, Nalpeiron5, or Nalpeiron6)
Choose the Force Quit [...]

If you are receiving an error message like this it can be due to the AST Service not starting up.  This service is part of our activation process.  You can start this manually.

Windows 7
This is due to the User Account Control (UAC) in Windows 7 being turned on. Please adjust the UAC settings (steps 1-5) [...]

With Windows Vista and Windows 7 there is a feature called User Account Control (UAC).  With UAC this prevents both versions of our plug-in from writing to the registry.  You have to deactivate under the version of Photoshop you first activated under.
If you cannot remember which version of Photoshop CS 4 you activated under you [...]

The serial number and license code are one in the same.  If you have any questions regarding your serial number or license code please contact customer service through the web or over the phone at 888-968-1468

No, the dashes are not required when you type in your license code.  You can type it in and the activation dialog will automatically do the rest for you.

If you are switching to a new computer or you’ve already activated your onOne product on 2 computers you can deactivate a copy to free up a license.  All you need to do is start up your product, and from either the Help menu or Photoshop menu select deactivate.  Do not choose to remove.  Removing [...]

Please download the file and follow these instructions for correcting this error.
1. Please close Photoshop
2. Download the zip file
3. Please unzip the downloaded file
4. Once the file has been unzipped, copy the ASTSRV.EXE file to the following location c:\Windows\System32
5. Please restart the computer, open Photoshop, and you will be able to launch PhotoTools