The end of the classpath should contain the com\gwt\client folder. That folder should contain the Attending.class file.
You don't add the package path to the classpath. The classpath points to the location of the package path.
Given this path: C:\folder1\com\gwt\client\Attendee.class
with the package: com.gwt.client.
Then the classpath should be C:\folder1

going up a couple of levels
If your current directory is client, you need the classpath to go up to folder1 to be at the start of the package path.