Assuming this is not just because your license/evaluation period has ended, if you find that SimericsMP has stopped working and opens with an error message listing a new hardware ID, the cause could be related to a change in your hardware configuration. The SimericsMP licensing system is tied to your network adapter configuration, and if that configuration changes, say by adding a new Ethernet card, your hardware ID will change. Some other things that may cause your network configuration to change are less obvious. For example disabling/enabling your Bluetooth network connection can cause SimericsMP to obtain a different hardware ID. Another example is installing software that adds a "logical" network adapter. This might happen with some network security software intended to restrict communication with untrusted web sites.
If you run into this issue, see if any of these situations may apply to you. Look at your network connections to see if there might be something new that was added or changed recently.