Once I start the launcher for Skyrim it does the usual loading of my mods and nonsense just like normal, but when I hit play and error pops up saying:

Your game is NOT supported, supported patches: 1.1.21.0 (31oct11)..................1.5.26.0
(the "......." is all patches in between)

I've tried defragging the cache files, verifying the game integrity, and uninstalling and re installing.

This error happened after I bought Dawnguard and I haven't been able to play since then... (bought it probably 2 days after it came out on the PC)

That message is generally from a script extender of some sort, or one of their plugins. Check to make sure they are updated or removed.

Looks like outdated ScriptDragon.

Here is the problem, I've tried uninstalling all my mods and trying and nothing happens... is ScriptDragon like an additional addon like program or something?

I'm still new-ish to the whole Skyrim on PC, used to be a console player for the longest time.

On a side note... Every mod I have ever had is in my data files in Skyrim whether the mod is subscribed or not, is that normal?

Check your Skyrim's root folder. This message is caused by an outdated script extender or one of their plugins.

I found it out, thank you for all the help. Much appreciated.