SLVbase is Silverlan’s Base, which is needed to run the T-rex addon.
Perriwen, I’ve had a similar problem with the T-rex, it got messed up, if I remember correctly, when I installed DansNPC pack (I THINK, it might have been one of the other packs, like Moarcombine). If you end up doing a reinstall, don’t put all your addons in at once. Do a couple (start w/ t-rex and whetever else got broken) and then test it, then drop out and add a couple more, then test again. Find out which addon is conflicting with what you want.
Also, just deleting Addons doesn’t work. They create models, materials, scripts, spawnmenus, anything else the programmer tells it to. Just because you delete an addon, doesn’t mean you’ve cleared up the conflicting code (and in my experience, deleting an addon without doing a little house cleaning (deleting spawnmenus especially) and a quick reinstall just breaks Gmod). Hope things get back up and running for ya!