The message "unable to contact sync engine" can appear for several issues. Here's the most common ones:
- Ensure you have a network connection that works. CMarks verifies there is network connectivity before starting a sync - but waits until the sync starts before attempting to contact Google. Check if you have a firewall/proxy server (for example) on your device/router/wifi connection that is blocking traffic or not working correctly (for example, some university wifi connections require you to login to a webpage first). CMarks needs access to "*.google.com" websites. Some countries (usually China) block access to various Google websites - I can't help you if that's happening unless you can use a vpn or proxy server.
- Ensure your device has the correct date and time. You don't need to be correct to the right second, but - for example - check the month is correct. If the month (and maybe the day) are wrong then some servers respond differently - a valid date and time are essential parts of how security works and validates on the Internet.
- If you have a hacked Play Store, or you cracked your version of Android to allow you to illegally use paid apps, please undo all of that - some of those changes *will* interfere with the normal functionality of CMarks and many other apps. The Full app uses enhanced SSL methods to allow the "write" functionality for the "read and write" of your Chrome bookmarks. The Lite app doesn't need this additional layer.
- For the paid app, most of these errors are due to bugs in the Android Play Store client (this can be proved as this error does not happen for the AndroidPit users who use a different Market client). If CMarks is failing for this error, other paid apps on your device will already - or will soon start - failing also. The solution is simple: Goto Android settings, Applications, Manage applications. Search for Play Store. Click on it and then "clear data". Then immediately reboot your device. Once restarted, open the Play Store, wait a minute for it to refresh itself behind the scenes and then try CMarks again.
- If you are using the paid app and you purchased from AndroidPit.com, then you might want to check that the login details in the AndroidPit App Center are correct and are for the account that you purchased the app from.