There has been a change made on your server that requires you to re-syncronise all it

[::Pixel.Freak::]

I'm getting this error about once every 2 weeks.

There has been a change made on your server that requires you to re-syncronise all items on your device. All changes made since your last successsful sync will be lost.

I understand that there are a lot of possible root causes for this problem, but what does it even mean and what is the proximate cause ? What steps should I take to diagnose this issue ?

[gadgetgaz]

I seem to get that error message when I sync to both my PC and my laptop. If I stick to just one there is no problem. It is very annoying.