All; I wouldn't consider that download from garrysmod.org safe.
Team Ulysses rarely if ever use garrysmod.com anymore for official releases.
Sure, it very well may have nothing changed or be wrong with it, but, unless we (Megiddo, JamminR, spbogie, jay209015, Stickly Man) link to it from here at the forums... it may not be safe to use.
And, as MrPresident said, and we've said hundreds of times in ulx_readme, FAQs and forum postings...adduser should be run from SERVER console or rcon if you've not followed the Garrys mod and ulx readme for adding yourself as admin.