I got a free license for my remote utilities account and now I would like to insert it in the 6.10.10 version of the software but I can't in any way because it always tells me that the key is not valid
Please note that the version 6 was discontinued for free license users - in order to use Remote Utilities with a free license, you need to update your installation to version 7. Here's a guide on how to update Remote Utilities (or you can also just re-install the latest version of the software). After updating, you can register your Viewer as described here.