If above fails:
Checking the Steam Master Server Updater log can provide more detailed information about the error. To do this:
Ensure your launch command line includes the proper parameters to enable master server communication. steam master server updater could not be located
Example for HLDS (GoldSource):
hlds.exe -game cstrike +maxplayers 16 +map de_dust2 +sv_lan 0 -port 27015 -secure
Example for SRCDS (Source):
srcds.exe -game cstrike +map de_dust2 +maxplayers 16 +sv_lan 0 -port 27015 -steam
Notice +sv_lan 0 and -secure (for GoldSource) or -steam (for older Source builds). On modern Source servers, -steam is often implicit, but adding it does not hurt.
steamclient.dll depends on Visual C++ runtimes. If missing, the DLL fails to load, causing the updater error. If above fails: Checking the Steam Master Server
After installation, reboot the server machine.