Question [Q] "App not installed" Humble Bundle

Got a call from a friend with a GT-N5110 Note 8.0 that I'm hoping y'all can help with.

Friend bought the latest Humble Bundle and tried to install Badland and ColorSheep using the HumbleBundle app. And then ran into two mistakes

Mistake 1 was that she didn't see the warning about turning on the "Allow install from 3rd party sources" first.

Mistake 2 was that she then got a prompt about turning this on for each game install, but didn't notice that there was a second tick box that said "For this install only" and didn't untick that.

Both installs failed with "App not installed" message. She's tried switching on that 3rd party sources and rebooting, but nothing gets those apps in. Weird thing is that ALL the other HB games install fine (after the reboot).

I've tried clearing out the HB's apps cache, sideloading the apk, but nothing works - I still get that "App not installed" message with no explanation WHY it's not been installed.

Is there some security cache somewhere that's not allowing these two apps to install or, failing that, is there some log I can check to see what the problem is with these two apps? I've tried logcat viewers but they don't give any info on software installs, and I've tried the APK's for those two games on my 2013 model Note 10.1 and they work fine.

I could try HB support, but I figure that this is probably one of those "deep in the engine room" kind of problems, so a shout out to the experts on XDA seemed more appropriate.
Current phones: LG G3 and Nokia 2330 Classic (works phone). Samsung GS III (with my youngest kid), Nokia N95 (being sold). SE P800i (worth nothing)
Tablets/PDAs: Galaxy Note 10.1 (1st gen), Asus Transformer, HP Zeen, 3xHP Touchpad 32GB, Nokia 770, Palm T3

And yes ... I DO look like my avatar!