TMG 2010 DNS_PROBE_FINISHED_BAD_CONFIG

Hi, I have:

TMG 2010
2 ISP
1 Domain
PCs + Servers

I have my 2 ISP connected to my TMG 2010 Server. The TMG is part of my DOMAIN and the others PC and Servers are part of it too, so they connect to internet through my TMG.

The problem is that SOMETIMES not always when I'm trying to connect to any website (not one in particular) it give me the next error "DNS_PROBE_FINISHED_BAD_CONFIG" it happens in every browser and every pc and just sometimes, not always.

Can someone help me? How can I fix it or search for a solution?

Thank you and sry for my english or inexperience in the field.