I am finally playing a piece of music that uses some of the very high frets like 17,18,19 etc. Am finding it quite difficult to play at speed around this area, because if I dont press down the string properly the note goes high pitched.

Any tips for playing around this area of the fret board?
What string gauge you using? It could be you could do with going down a size.
But the majority of it will be just getting your finger strength up. Practice practice practice. The old cliche.
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Everton FC
The strings are 9's, an example would be: I would be playing on the B string 17 fret then the next note would be the 17 fret on the high e string. So what I do is just barre the 2 strings at the 17 fret. But one note sounds fine and the other sounds high pitched.
Your probably not fretting it correctly. either this or your pushing the string off the fretboard. this can sometimes cause it to go up in pitch.
Just work on your finger strength and check that your pressing down both the strings correctly onto the fretboard.

Your string gauge is fine.
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Everton FC
i dont understand what you mean by it sounds high pitched...of course it does, your going a string up on the same fret....explain please..
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As far as i know the only liquor that should not be stored after opened is wine, and even then it's mainly the french one. American wine usually has conservatives in it to stop this.
Its meant to sound normally pitched but when barred the pitched on that fret on that string increases, when its not meant to.
You just need to practice playing on that part of the fretboard. It isn't quite the same as playing lower on the neck. Just because you can play the A minor pentatonic in the 5th position doesn't automatically mean you can play it just as well in the 17th position.