Hi @daviddamian. I believe there is a bug in the new release of Arduino SAMD Boards that causes this:
Arduino's developers are already working on a fix. Until the next release comes out wiith that fix, the workaround is to install Arduino SAMD Boards 1.8.9:
- Tools > Board > Boards Manager
- Wait for the updates to finish.
- From the list of boards platforms, click on "Arduino SAMD Boards"
- From the "Select version" dropdown menu, click on "1.8.9".
- Click the "Install" button.
- Wait for the installation to finish.
- Click the "Close" button.
Now you should be able to update your firmware without getting the error.
Since you likely only need to update the firmware once, after doing so, you can upgrade back to 1.8.10 by repeating the instructions above, but this time updating to Arduino SAMD Boards 1.8.10 again.