Can you give us a little more detail? Is it a popup message from the Gallery app?
On the stock Android Gallery app, you can turn off syncing with Picasa by going to Settings>Accounts-Google>[your Google account], and unchecking Google Photos (not Google+ Photos). Google Photos is what syncs your Picasa/Google+ albums to the stock Gallery app. In some devices, it might be listed as Picasa instead of Google Photos.