Hi Ray,
Do you have all your Windows updates installed? Pay special attention to make sure you have .NET 3.5 installed.
If you already have .NET installed and have been able to run the client until recently, then here are some steps that should help clear the problem.
1-Remove/uninstall the client from your system.
2-Delete the following folder: C:\Users\username\AppData\Local\Apps\2.0\ (delete 2.0)
3-Download and install the latest version from our website.
4-Generate a new API key. If you are going to copy/paste the key, make sure you do not include blank spaces.
Let me know if this resolves the problem or if you require additional assistance.
Thank you,
Chad | Entropia Life Support Team