I can still load VO directly, but it seems there is an update on the play store waiting, that will not install.

I get the error "Vendetta Online can't be installed on USB storage or SD Card. Try again, blah bah (Error code -18)"

VO is not installed on USB or SD card, it is installed on my internal memory. This is a kitkat device, so my internal memory is mapped as /sdcard or as /storage/emulated/0 - my sdcard is /storage/sdcard1.

Anyway, do not want to uninstall at this point as it still works (but will if advised to), previous updates installed no problem, and I have over 2GB of internal space left so space is not an issue. I have not made any changes to my device (no new apps, no move to sd apps or anything else), so I have no idea what has changed.

Is this a Google Play Store error? When did this start happening for you?

Yes, its a play store error. Started happening the day of this thread, I normally have all my apps update when I am on WiFi, and this is the first time I've had a problem with VO. Had another mess around with it last night to see if I could resolve it. Rebooted the device into recovery and cleared caches, cleared the data from the VO app, nothing seems to work.

[edit]

I have unistalled vo, restarted the device, and installed it again. It seems to work fine now? No idea what caused it, as my device (Galaxy S4 Mini) does not support running apps from SD natively and I do not have any "move to sd" apps installed.

Weird, but it is working now.