What happened to the UML menu?
The UML menu can disappear when Microsoft Office Visio encounters an unexpected error from either an internal or external source. To recover it try the following:
Restart Visio if it shut down unexpectedly.
On the Tools menu, click Options.
On the Security tab, select the Enable Automation events check box, and then click OK.
The new setting will take effect after you restart Visio and reopen the UML Model Diagram template.