This is how I fix this error on my machines. This error usually occured after I updated a machine to Lion after "Sync Yahoo Contacts" and "Sync Google Contacts" were being used in Snow Leopard.
Basically what I think is happening is that when you first login to your account (on your mac, after upgrading to lion) it ask you "Hey sign up for iCloud." Most people do this right away, as do I. Thing is I think iCloud does a bad job disabling these two syncs (well just one actually - Yahoo).
What you need to do is goto Address Book, and PULL down File -> Preferences. In Preferences click on Accounts. At this point you probably have iCloud and On My Mac. Depending on how you want to do a quick backup, you can go to the iCloud tab and turn off the iCloud check mark, you are not loosing your contacts you can enable it again and they will be right there. It's just basically showing them and hiding them. After you disable that, you should just have On My Mac (contacts).
Click on a contact and then PULL down Edit -> Select All. After that PULL down File -> Export Address Book.
I ditched my Yahoo, and you can too. You can re-import them later if you want (Apple does not recomend syncing with Yahoo and iCloud or anybody else as far as I know, but for now after I exported them, I PULL Edit -> Delete Cards. This is AFTER BACKING THEM UP.
Then Go back to the Preferences Tab -> On My Mac and click "Syncronize with Yahoo" basically renabling the sync again. After you sign in, and are done the sync, the sync menu should show, (secret: you could goto Core Services if you want but...) . It should spin a while and then they are Synced erasing them or not depending on how you feel about your Yahoo contacts. Remeber you can do this over and over and re-import etc.
After you are done syncing Go back and Turn off the Yahoo Sync again, in Preferences -> On My Mac, then goto the iCloud tab and click on "Enable this Account"
To make a long story short (but you should read this tho for backup) You need to reenable sync then disable sync with Yahoo manually in Lion after a Snow Leopard upgrade.
You should have all your contacts from iCloud right there now. One extra thing. PULL File -> Preferences -> General Tab, then click on Default account tab and make sure it is on iCloud. This way whenever you make changes they will goto you iCloud account.
This should get rid of it (the annoying pop up). If you goto the sync menu it should say "No Devices Syncing" and stop the pop-up. If you want you can Apple Key Click on the Sync Menu and Drag it away to trash it.
Laters... and Lagers it's the Weekend with NBA even the games kinda suck...