I’d been having issues recently - not being able to create a manual cache as has many other people it would seem!
So after not being able to find a fix, I started to play around to see what I could do and whaddya know… I fixed it!!!
The problem arises when the manualcahe.ccc file is previously deleted.
Fix:
Make sure the sim isn’t running.
Create a rolling cache.
Locate the file generated by that rolling cache (ROLLINGCACHE.CCC)
Copy it and paste it into:
C:\Users[your username]\AppData\Local\Packages\Microsoft.FlightSimulator_8wekyb3d8bbwe\LocalCache
Once copied, rename the file to “MANUALCACHE.CCC”
Reboot- SORTED 