Sometimes if a back up fails or for some other reason you SharePoint sites can site can be left quiesced and/or the site collections and central admin site will be locked.
Some of the symptoms of a quiesced or locked farm or site can be a failing content deployment, or users complaining that they can’t edit and have lost their permissions.
Unlike SharePoint 2007 you can no longer unquiesce a farm through central admin unless you add a custom solution such as the one from estruyf .
You have to use PowerShell. Here is the command.
stsadm -o unquiescefarm
Even after running the above command I have still found that some of sites (including central admin) are locked.
You can check you site collections and central admin site are not locked by running the following command
stsadm -o getsitelock -url http://<site>
You can update/unlock using
stsadm –o setsitelock –url http://<site> –lock none