supposedly, you need to hire a Guatemalan guide in Tikal. You can't bring a guide from Belize. At least that's what they told us last week. Perhaps its an informal arrangement with the hotels and the Tikal park?
There were some border problems 2 wks ago due to Belize hotel vans bringing tourists into Guatemala. We got through OK, but 2 days later the border was closed for 2 days because the Guatemalan gov't apparently wants free trade; for Belizean hotel vans to stop at Melchor and for you to have to take a Guatemalan transfer to Tikal from there, similar to the way the buses run.