I have also been having problems with licensing errors while in boot camp. I have been able to run AutoCAD Revit w/ no issues in Parallels. However,I can certainly understand why some don't want to run on Paralells. Parallels in Virtual and is not able to access my 512 mb NVidia 8800 GT graphics card and it appears quite difficult to link it to my plotter and also defaults to 512 Mb RAM. This doesn't work well with my Apple Cinema 23" screen. I have tons of RAM doing nothing in Parallels, when my AutoCAD Revit is the software program that needs the most RAM of all of my software. So I prefer running Windows "natively" on Bootcamp. It is much faster, no comparison.
I have had similar licensing issues on Bootcamp and here's what has helped.I had read other blogs that blamed the clock, external hard drive and boot order.
First, upgraded with the new Bootcamp update that was released in preparation for the release of Win xp sp3. In fact, Apple says you need to update Bootcamp before updating w/ Win xp sp3. This update solved my bluetooth mouse and keyboard problems ( going in and out of commission). Next I put the Windows XP partition as my default boot. So now when I turn on my MacPro and it boots up it boots into Windows, and I access Mac by shutting down and then boot up w/ option key held down to get the boot screen and choose Mac. This solves the clock problem. ( If Mac is the default o.s., then Windows boots up and its clock reads 4 hours later for 5 seconds before showing the actual time.)
So after doing these things, I then loaded AutoCAD REvit 2008 (re-auth.), and loaded some updates that my Autodesk reseller suggested and the computer glitched. I had to force quit the CPU and restart. When I opened the AutoCAD Revit software I got the re-authorize message.
So..Here's what I did differently next time: I loaded AutoCAD Revit Building 2007 first (re-authorized) b/c I wondered if it had to be on the hard drive first, and it has (Revits 9.1 COM New) on the label and I noticed that the AutoCAD Revit Architectural Suite 2008 has (Revits 2008.0 COM Upgrade from Revits A, SUBM:RAC-S 2008 DVD LIC UPG.) I was never told that it was an upgrade! So I think I may always have to have the 2007 version on the hard drive first and then the subsequent upgrades. I didn't REALIZE that the 2008 version of AutoCAD Revit was an upgrade b/c I have the software by itself on my HP laptop w/ no problems. I never had to load both. Before you go OH Well... However, I still think I may be having imcompatibility issues w/ the external Maxtor hard drive. When loading the 2007 version and opening from the external hard drive and leaving the hard drive open when closing out the 2007 AutoCAD Revit, I got an license error message after that,when re-booting into AutoCAD Revit, and it gave me the screen that asks if you want to authorize or continue use for 5 days, and I hit authorize. It then opened normally, not in the authorization menu! So I think it saw the license, but there may be a glitch w/ Bootcamp and AutoCAD Revit and that external hard drive. After I was able to open the 2007 version normally several times,turning the machine on and off, I went ahead and loaded the 2008 version and the updates that the reseller gave me links to w/ no problems. So far , so good. I am being careful to open the Maxtor hard drive after I load AutoCAD Revit and turn it off before I close and leave it.
After all this, I have to say, update everything, be sure you have a Full Version (of your License) Autodesk software, and be careful about hard drive incompatiblity. Autodesk has acknowleged incompatibility issues w/ some usb external drives. However, I don't have any issues on my PC or win/ laptop w/ same hard drive when in AutoCAD REvit.