Hi, my vintage v300 acoustic guitar plays well enough but for some reason whenever i hammer on at the 12th fret or higher it buzzes and the note can hardly be heard. If i just fret the notes at the 12th and higher they are fine!

What could be the problem and what could i do to try and rectify it? thanks
Are your frets level?
Strings crapped out?
Main Gear:

Santiago S3 Spanish Classical
PRS CE22 Mahogany
Mesa/Boogie F-50 combo w/ G12K-100
Teese RMC Wizard Wah
Rothwell Switchblade
Ibanez FL-9
Visual Sound Liquid Chorus V2
Quote by jimtaka
your frets aren't level? not flat... level.

whoops, yes they are level and no the strings haven't crapped out