It's been referenced in other posts a long while back, but I'm putting it here, also. Insider build 14342 is the first build where I have had an issue adding the Optional Feature .net Framework 3.5. It fails with one of the following error codes:
0x800F0906, 0x800F081F, 0x800F0907

It tried to download the files for the feature, but was unable to locate them on any MS server.

There is an excellent MS article explaining and giving resolutions.

https://support.microsoft.com/en-us/kb/2734782

I used the mounted ISO created from the install.esd of 14342 and ran the following command at admin cmd:

DISM /Online /Enable-Feature /FeatureName:NetFx3 /All /LimitAccess /Source:d:\sources\sxs



Where the Source:d was the mounted ISO drive letter I used to do the tech review installation. You could use a DVD, also.


Hope this helps anyone who has encountered this issue. TC