Weird DNS Problem

We are inside an MPLS network, and for the last week or so i been having issues with accessing random websites.
For example today, i cannot access www.budget.com if i use our internal DNS, now if i DHCP and get DNS from ISP, it works.
I tried to nslookup several other sites and have no problem getting an answer, but if i try that particular website, POW! Nothing. can’t find server.
All this happens when i use internal DNS.
I got no DNS errors in log, nothing seems to be out of place.
Of course if i add ISP DNS as secondary, it works!
Anyone out there that can give me fresh ideas?
Thank you for your time.