I have source since more that 2 or 3 months, and i never had that error before, today, half life 2 deathmatch had an update, and i created my server via "create server" in the escape menu ingame, like i do everydays, and i tried a source op command like +jetpack, and it said:

unkown command: +jetpack
unkown command: -jetpack

at the beggining of the console, it says aot of source op loading, (normally), but now, it say:

Can't find sourceop.dll on disk

in red.