This is a known Bentley issue that is not specific to Axiom products.

Error header: Microsoft .NET Framework
Error body: Unhandled exception has occurred in a component in your application. If you click Continue, the application will ignore this error and attempt to continue.
Illegal characters in the path.

If you're seeing this error when selecting a product from the Axiom menu, you're encountering a known Bentley issue. The issue is not with Axiom products. We've reproduced the same behavior when launching Bentley-delivered applications.

We’ve created a new Axiom menu that works around the issue. All you need to do is download and install the latest version of your Axiom software from this link:
Download Axiom Products for MicroStation V8.