Try this... there is a slight error in lines 29, 30 and 31 with the variables.

On $*:Text:/(^[\+-])ytdetect$|(https?\x3a\/\/|www\.)(([\S]*youtube\.com[\S]+v\=)|(youtu\.be\/))([\S]{11})/Si:#: {
  var %tion $strip($regml(1)), %id $strip($regml(4))
  if (%tion isin +-) && ($regex($nick($chan,$nick).pnick,/(!|~|&|@)/)) {
    if (%tion == +) {
      if ($istok(%LinkDetectorForYoutubeChanList,$+($network,$chan),32)) { .msg $chan $nick $chan is already running the LinkDetectorForYoutube script }
      else { 
        .enable #LinkDetectorForYoutube
        set %LinkDetectorForYoutubeChanList $addtok(%LinkDetectorForYoutubeChanList,$+($network,$chan),32)
        .msg $chan $nick has activated the LinkDetectorForYoutube script for $chan .
      }
    }
    else {
      if (!$istok(%LinkDetectorForYoutubeChanList,$+($network,$chan),32)) { .msg $chan $nick $chan is not running the LinkDetectorForYoutube script }
      else { 
        Set %LinkDetectorForYoutubeChanList $remtok(%LinkDetectorForYoutubeChanList,$+($network,$chan),1,32)
        .msg $chan $nick has deactivated the LinkDetectorForYoutube script for $chan . 
      }
    }
  }
  elseif (!$timer($+(LinkDetectorForYoutube,$network,$nick))) && ($istok(%LinkDetectorForYoutubeChanList,$+($network,$chan),32)) {
    .timer $+ $+(LinkDetectorForYoutube,$network,$nick) 1 4 noop
    GetLinkDetectorForYoutube .msg $chan %id
  }
}

It worked for me when I changed it. > [7:18pm] <~Stewie> +ytdetect
[7:18pm] <&thunderbolt> Stewie #i is already running the LinkDetectorForYoutube script

Yea, I had tried that before, realizing that the variable wasn't supposed to look the way it does. The original variable's name is %action and somehow it became ¬tion in the script above - but correcting it doesn't change anything. This newer version of the script still doesn't work for me, when all I do is copy&paste it (and change the variable in those 3 lines).
Thanks for trying to help though!

When you view the 'Variables' page... is something like this in it > %LinkDetectorForYoutubeChanList Torn#i if not, maybe you could try adding the channels manually, just until you can get the +/-ytdetect to work. Also, you do have OP status or above in the channel, right? It won't work for the +/-ytdetect if you don't.

Thanks, that fix worked. Do you by chance know how to make likes/dislikes work again? :)

Try this:

On *:sockread:LinkDetectorForYoutube*: {
  if ($sockerr) { sockclose $sockname | return }
  else {
    var %LinkDetectorForYoutube | sockread %LinkDetectorForYoutube
    if ($regex(%LinkDetectorForYoutube,/<span class="likes-count">(.*?)</span>/i)) { 
      hadd $sockname likes $+($hget($sockname,tagcolor),Likes:) $+($hget($sockname,textcolor),$regml(1)) 
    }
    elseif ($regex(%LinkDetectorForYoutube,/<span class="dislikes-count">(.*?)</span>/i)) { 
      hadd $sockname dislikes $+($hget($sockname,tagcolor),Disikes:) $+($hget($sockname,textcolor),$regml(1))
    }
    elseif (<span class="watch-view-count"> isin %LinkDetectorForYoutube) {
      hadd $sockname viewsFound 1
      if ($regex(%linkdetectorforyoutube,/\/user\/([^\/]+)\/videos/i)) {
        hadd $sockname uploader $+($hget($sockname,tagcolor),Uploader:) $+($hget($sockname,textcolor),$regml(1))
      }
    }
    elseif ($hget($sockname,viewsFound)) {
      hadd $sockname viewsFound 0
      hadd $sockname views $+($hget($sockname,tagcolor),Views:) $+($hget($sockname,textcolor),$remove(%LinkDetectorForYoutube,<strong>,</strong>)) 
    }
    elseif (($regex(%LinkDetectorForYoutube,/dir="ltr">(.*?)<\/a><span class="yt-user-separator">/i))) {
      hadd $sockname uploader $+($hget($sockname,tagcolor),Uploader:) $+($hget($sockname,textcolor),$regml(1))
      hadd $sockname date $+($hget($sockname,tagcolor),Upload Date:) $+($hget($sockname,textcolor),$regml(2))
    }
    elseif (($regex(%LinkDetectorForYoutube,/watch-video-date"\s>(.*?)<\/span>/i))) {
      hadd $sockname date $+($hget($sockname,tagcolor),Upload Date:) $+($hget($sockname,textcolor),$regml(1))
      if ($hget($sockname,tags)) $gettok($sock($sockname).mark,1-2,32) $hget($sockname,logo) $Xchr($regsubex($v1,/([\S]+)/g,$hget($sockname,\t)))
      if ($hget($sockname)) hfree $sockname
      sockclose $sockname          
    }    
    elseif ($regex(%LinkDetectorForYoutube,/class="watch-video-date"\s>(.*?)<\/span>/)) {
      hadd $sockname date $+($hget($sockname,tagcolor),Upload Date:) $+($hget($sockname,textcolor),$regml(1))
    }
    elseif ($regex(%LinkDetectorForYoutube,/class="long-title".*title="(.*?)">/)) {
      hadd $sockname title $+($hget($sockname,tagcolor),Title:) $+($hget($sockname,textcolor),$regml(1))
    }
    elseif ($regex(%LinkDetectorForYoutube,/<meta\sname="title"\scontent="(.*?)">/)) {
      hadd $sockname title $+($hget($sockname,tagcolor),Title:) $+($hget($sockname,textcolor),$regml(1))
    }
  }
}

[6:45pm] <~Stewie> http://www.youtube.com/watch?v=kHeMck0Ap3I
[6:46pm] <&thunderbolt> YouTube Title: Amaranthe -Razorblade Views: 1,583 Likes: 19 Disikes: 1 Uploader: Luis Manuel Oviedo Vizcaya Upload Date: 23 Mar 2013

awesome. I tried to figure it out myself and had something similar, but it didn't work. You're the man, thanks.

You're welcome mate. :)

Yes, I know about %LinkDetectorForYoutubeChanList.

TL/DR: I'm out of ideas - but I'll just use the working version of the script that I have.

So... this version of the script is not working at all for you? :(