The version of our software which is installed on your terminal must match the version of registration keys which you are using. If these do not match, the registration will fail. As an example, version 5.1 keys will not work with version 5.5 of our software.
To find out the version of our product installed, run it. Now select File -> About. The screen shots below are from About dialogs for both Windows Mobile and Window CE OS platforms. The version number, build id and build label are clearly shown.
To find out the version of registration keys, refer to the License Keys email which you should have received. A sample of this is shown below with the key version number text circled in red. You can also open the license.xml file and look at the comments which clearly start the version of the registration keys.