There are many resolutions depending on what the error is exactly. They could be failing because of space issues or any number of reasons. Please provide the details when asking a question of this nature. I work a lot with WSUS and can help with resolutions but only if the details are provided along with what troubleshooting steps you have taken. Thanks.
Review log entries from the WindowsUpdate.log for the scheduled installation event, and determine exactly what client system. Also check what updates r scheduled for installation, if any. To identify the actual error:
Open a command window.
go to WSUSInstallDir\Tools
type wsusutil checkhealth
Now check the Application log for the most recent events from source Windows Server Update Services and event id 13000.