The Grand Theft Auto V patch released yesterday fixed a lot of bugs, but it also had the unfortunate side effect of breaking mod functionality. The problem, according to GTA5-mods.com, is that the patch makes changes that renders Script Hook V unusable, and no Script Hook V means no script mods.
Fortunately, it's possible to re-enable Script Hook support by downgrading to the previous version of the game. Just download the requisite files as explained at GTAforums.com (or use your backups, if you're fortunate enough to have them), and then copy them back in place. It's not a perfect fix, however; downgrading will get your mods working again, but you'll only be able to play offline.
And it doesn't look like that situation is going to improve anytime soon: Script Hook creator Alexander Blade wrote that a new version of his mod-enabling software is in the works but warned that it won't allow users to go online at all. He said the restriction is an attempt to keep players from being banned, even in single-player mode.
"Starting with this patch if the game will detect that you have mods (in any way) while being Online it will report this to R* servers," he explained in a separate post. "Guess what will happen next."
We've reached out to Rockstar for more information, and will update if and when we receive a reply.