This problem is caused by the UAC feature newly introduced with Windows Vista. Try the following solution please.

Shutdown NetLimiter client application (the main NetLimiter window) and then run it as administrator. For example, you can do it by right-clicking the NetLimiter desktop icon and then choosing the Run as Administrator menu item.

To avoid this problem on next system startup, you can set permissions for your user account . In NetLimiter, start permission editor (Menu View->All Tools), find your user name in the list and then check off the monitor and control rights.

Next version of NetLimiter will solve this issue (the current one is 2.0.9).