SharePoint: Installation Required and Upgrade Blocked
Definition
When we install the CU in the farm, we see the installation required and upgrade blocked in the status of servers under the system settings in CA.
Installation Required
The server still not yet installed with the same CU that is already installed on other servers.
Upgrade Blocked
The server is blocked from the upgrade. The current server is installed with latest CU and it will remain blocked until all the SP servers in the farm are installed with the same version.