A new version of RevMob that is RevMob 5.2.7
has been released recently. Upgrading to this version might solve your problem.
EDIT:- RevMob is working absolutely fine in Testing mode but giving the same error as you mentioned above in production mode. I have tested it on device as well as on simulator.
EDIT2: I contacted to RevMob team regarding the issues and got the below reply:
This message is normal. Don't worry.
It either means that currently there are no apps to be promoted in your device or you have already downloaded all the available apps at the moment.
If you want to make sure integration was done properly, you can use our Testing Mode (http://sdk.revmob.com/). But make sure to turn it off before submitting the app ;)