This error occurs when you attempt to access an "unsafe" property or invoke an "unsafe" method. An "unsafe" property or method is one that can potentially damage your system if invoked.
Currently, the only time this error can occur is when you attempt to invoke the Toolbar object's SaveSettings and RestoreSettings methods. These methods are considered not safe because they allow you to write to the Windows registry.
The only time you should see this error is when the control is hosted by a safe environment, such as Internet Explorer.