There was an issue with the Telerik Verified Plugins Marketplace at the time of you writing. It was due to a bad plugin submitted there. We managed to workaround the problem and I believe the matter should be fixed on your side now. Please, let me know if the issue still remains and accept our sincere apologies for any inconvenience caused.
About the LiveSync, could you please share a bit more information about what exactly is failing inside your projects? Also, in which AppBuilder client and on what platform (iOS, Android, WP)? Thank you for the help in advance.