I am frustrated to hell and back. Here's the history.
Running i72600 3.4 GHz, 8 GB RAM, (clears throat) nVidia Geforce 9600 512 MB (hey I got the rig as an upgrade and had to port over some essentials like the graphics card

), Windows 10.
1. I recently migrated to FSX SE after 8 years of boxed edition sp2 + accel. I had Captain Sim 777 base pack and Expansion running perfectly.
2. After installing FSX SE tried to migrate by simply copying addons

Obviously not going to work. No guages and landing gear
3. I installed version 1.4 which was the last one I downloaded and she showed up with everything appearing to be okay.
THIS IS WHERE IT GETS INTERESTING
4. I loaded up a flight Speedbird 2255 EGKK-TBPB FL360 initially using the CS 777-200GE. Everything went smoothly until on the flight route between GIBSO and DAWLY on the UL620 passing FL310, I noticed the aircraft not tracking the center of the magenta line. She was a bit right of center and crabbed ~5 degrees to the right. Within 4 mins later she lost it. She went into a a shallow right bank, departing the flight track completely. This got progressively worse until she was hard stuck in a 30 degree right bank. Not a problem. Use heading select to get her back on track and try LNAV again right? I discovered that ALL LATERAL AUTOPILOT CONTROL WAS NOT FUNCTIONING. Heading hold, heading select and LNAV did nothing to alter the right bank. Hand fly her back to the line, choose direct to the next waypoint on the FMC. Click LNAV again. Nothing! Selecting heading select or heading hold does nothing. The right bank comes right back. Lights on on the MCP, and mode status appears in the MFD but no change in the right bank. I ended up counting 5 right 360's over the english channel. Had to cancel the flight and return her to Gatwick by hand. Not very many happy holiday passengers in the back I can tell you that.
5. A little research online showed there was a version 1.6 which was an update especially for FSX SE. One of the fixes mentioned was "TRK hold issue fixed." Well there you go! There's your problem! Installed the update. Loaded the aircraft same problem.

6. I wondered if it was a problem with the route so Operations instructed me to fly the aircraft to their maintenance base in Cardiff for a fix. Flew EGKK-EGFF FL120. She followed the route without incident.
7. At Cardiff, technicians discovered another software update that was not done. "FSX-SE-777-Migration.exe" Well we loaded that and we are not even sure if it installed or not because of the cryptic message which looks like this
AND SINCE I CAN'T POST AN IMAGE AS THIS IS MY FIRST MESSAGE - I'll have to say it says "exception caught. Completed, press any key to exit"
8. Flew her back to Gatwick at FL210. Again she tracked the route percectly and heading select vectors worked fine.
9. I have tried EGKK-TBPB no less than 5 times and the same issue happens at the same point. I have even tried a different route KMCO-KJFK and round about above FL300 the same right bank departure happens.
10. What is worse I cannot find ANYTHING ANYWARE on this issue. Surely I cannot be the only one experiencing this problem.
11. So in brief here is the problem summarized. Passing FL300 all lateral navigation modes, LNAV, Heading Hold, Heading Select, becomes unresponsive and the aircraft enters a shallow at first right bank that then proceeds to a 30 degree bank either indefinitely or progressing to 60 degree bank until it noses over.
12. Sent an email to CS on their general email address after searching hopelessly for a means of contacting customer support.
13. I did do a clean uninstall of CS777 and reinstalled. No luck.
14. Did I try the -300 model to see if it does the same thing you say? Well the I loaded -200GE in American Airlines livery and the -300GE in Air New Zealand livery and I had no gauges and landing gear...so

But that's for another forum, right?

I will appreciate any help and I hope the answer is obvious and I missed something.
Cheers!