The SCM Sync Configuration plugin has been failing for a while.
Here's what is in the log file:

{{ul 28, 2016 9:36:09 PM INFO hudson.plugins.scm_sync_configuration.ScmSyncConfigurationBusiness
Queue of changeset A hudson.model.UpdateCenter.xml
aborted (scm manipulator not settled !)}}
and followed by a list of the same error...
At first I thought it was authentication issue with the repository, but I followed the troubleshooting page and created a test job. It successfully authenticate with the repository, which means it should have no problem access it.

I also checked your source code and found that the message would occur when calling the queueChangeSet() }}method in {{ScmSyncConfigurationBusiness.

Tried a lot of ways mentioned online such as restarting Jenkins...

Also when I tried to hit "save" in Jenkin's configure system, it always took a lot of time and then gave me an error.

So, much appreciate it if anybody have any insight into this.