URL categories removed

Hello,

I have a Policy Server working with 2 Filtering servers: one in Squid Integration (working well) and a new one in Stand Alone mode (with also Network Agent installed). During the night I have received a warning mail saying "URL categories removed from master database" from the Filtering Service in Stand Alone mode. The list was full of all categories of Websense (about 100).
From the statistics I see 0 blocked pages from the stand alone server (even if all the traffic is visible to the Network agent)
Any help?

Thank-you, Roberto
I'm using Websense Enterprise 6.1