There are a couple of different things you can try to see if the problem clears up for you:
1. Verify the integrity of the game files: To verify game file integrity for Steam games (instead of uninstalling and reinstalling), you can right-click on the game found in your Steam Library, select “Properties” from the drop-down menu that appears, click on the “Local Files” tab, and then click on the “Verify Integrity of Game Cache…” button. Any files for the game that are missing or corrupt will be replaced.
2. Firewall and anti-virus settings: Allow the file “eoa.exe” to access the Internet by modifying the firewall and anti-virus settings on your PC.
If you continue to get an exception error when launching Myst V after trying these suggestions, please contact support and we will troubleshoot the issue further.