Is your copy of Acrobat up to date with version updates?
The current version is 9.5.1.
Did you create the dynamic stamp?
Have you completed "Identity" category in Acrobat's Preferences?
Do the Dynamic stamps supplied by Adobe work?
What is the code you are using to insert your name?
The code supplied by Adobe for their Dynamic stamps:
event.value = (new Date()).toString();
AFDate_FormatEx("h:MM tt, mmm dd, yyyy");
event.value = "By " + ((!identity.name || identity.loginName != (event.source.source || this).Collab.user) ? (event.source.source || this).Collab.user : identity.name)
+ " at " + event.value;