Please, ensure that .Net 3.5 is installed on the target computer.
Hi sorry for not getting back to you before.
I see that both Windows 8 / 8.1 and 10 no longer have .net 3.5 included - I guess this goes for server too but I have yet to roll out as far as servers.
I ended up using some group policy "Computer Config>Polices>Windows Settings>Scripts>Startup pointing to a pair of BAT files on a UNC share path - note that the bat file must have security set for read/execute "Authenticated Users"
so the client machines can run it as "System". The GP then has some WMI filtering enabled so it only runs on the correct machines:
For windows 10
select * from Win32_OperatingSystem where Version like "10.%"
select * from Win32_OperatingSystem where Version like "6.3%"
The BAT file's for us one for 8.1 and one for windows 10 had the following commands which point to the extracted sxs folder for each source ISO:
Dism /online /enable-feature /featurename:NetFX3 /All /Source:"\SERVER\ISO\OperatingSystems\Windows10 Enterprise x64\SW_DVD5_WIN_ENT_10_64BIT_English_MLF_X20-26061\sources\sxs" /LimitAccess
Dism /online /enable-feature /featurename:NetFX3 /All /Source:"\SERVER\ISO\OperatingSystems\Windows 8.1\SW_DVD9_SA_Win_Ent_8.1_64BIT_English_-3_MLF_X19-84068\sources\sxs" /LimitAccess
Then on login the missing feature is installed and like magic the custom WPP updates will work a treat.
I hope this is of some use to other newbs to WPP like me setting this up for the first time,