Lansweeper pulls license keys from the client machine's registry. If an incorrect key is stored in the registry, there is nothing we can do to resolve this issue.
Make sure you are running the latest Lansweeper release. There were some bugs in previous releases that could cause keys to be incorrectly read from the registry. Update instructions can be found on page 176 and beyond of our online documenation: http://www.lansweeper.com/documentation.pdf