"Invalid host" is a variation of the "Invalid or missing license file" errors. It indicates that FLEXlm (the licensing software used by Maple) is reading a different Host ID (or Disk Serial Number) than the one in the license file (created during activation of Maple). This could happen, for instance, if you upgrade your operating system, or the order or addresses of your network interfaces has changed.
If you have an additional activation remaining, you can simply reactivate Maple. Please note, however, that this will decrement the number of activations available for your Purchase Code.
If that is not an option, please contact Maplesoft Technical Support, by filling out a support request.
If we determine the license resilience can be improved by incorporating other hardware identifiers from your system, we may ask for your complete Host ID information, including your read host ID, while your network connections are off.