@wayne-workman i managed to go from 16 to 18 (server) fine… but when i tried to go 18 to 20 it all went wrong so just rolled the VM back. i will when 18 falls out of support do what Seb suggests and move the images over and the DB to a fresh install… after all my VM started life as v 14 of ubuntu so probably due a fresh install.

Best posts made by Gordon Taylor
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RE: Which Linux distro(s) have been tested with FOG - What is recommended?
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RE: Unable to encrypt drives with bitlocker after deploying image with Fog
@ITCC Someone much more cleverer than me (from ANME) has worked out how to fix it and it is due to sysprep sealed images rather than Fog persay as Tom suggested. the Fix is to add the following to your sysprep SetupComplete.cmd file
for /f "tokens=2 delims={}" %%a in ('bcdedit /enum {bootmgr} /v ^| find "identifier"') do set prep-bcdid={%%a} bcdedit -set {current} device partition=c: bcdedit -set {current} osdevice partition=c: bcdedit -set {memdiag} device partition=\Device\HarddiskVolume1 bcdedit -set %prep-bcdid% device partition=c: