Authorization Manager (AzMan)

I am using AzMan for User Authorization.

And sometimes I am getting this error:
A required privilege is not held by the client. (Exception from HRESULT:
0x80070522)'

This error happens at:
AzAuthorizationStore azManStore;
azManStore = new AzAuthorizationStoreClass();

// Initialize AuthMan
azManStore.Initialize(0, azManConnectionString, null);

Application is WCF Windows Service, and for each call to the service it
makes call to the AzMan to authorize user if s/he has rights for the method.

Application is running on Window 2003 server SP2.
AzMan storage is used as xml file.

I cheked checking CPU and it is about 1-2% load.

Lately when we started to receive more traffic I started to get more and
more this errors, please help on this.

Thanks a lot.

Sincerely,
Vlad.