Do you have a prefix in the same group to go with it?
Prefix/suffix commands must always consist of two parts: The prefix, and the suffix.
E.G. you'd have "my name is" as a prefix, and "what", "who", and "chicka chicka slim shady" as suffixes, allowing you to combine the former with the latter, as in "my name is what", or "my name is who", and so on.
If you want to dictate your name instead(meaning having the speech engine make a best guess at what you're saying, not necessarily letter-by-letter), you need to use a normal command with wildcards(wildcards are not supported for prefix/suffix):
E.G. "my name is*"
This command can be executed by speaking "my name is", followed by a number of words.
E.G. "my name is Maximus Decimus Meridius" would be recognized.
You can then use the "{CMD_AFTER}" token to get whatever came after the wildcard:
Say, 'Your name is {CMD_AFTER}'
Which given the above example would say "Your name is Maximus Decimus Meridius".
For more information on the use and limitations of wildcards, check page 18 and 19 of VoiceAttackHelp.pdf, which is included with your installation of VoiceAttack(If you press F1 while VoiceAttack has focus, it should open in your default PDF reader).