i have After Effects CS5 and when I try to import AVCHD file into my composition it wont let me it says:
After Effects error: file *****.MTS cannot be imported --- this '.mts' file is damaged or unsupported.
but i know for a fact that the file is fine i can play it on windows media player and quicktime perfectly so i dont know why it wont work
so to put it simply;
why wont After Effects CS5 import my AVCHD / mts files?
Either it's from an unsupported camera or something else is going on on your system, in particular potential CoDec conflicts. Eitehr way, you need to provide much more info.
Any highly compressed original should be transcoded into a production codec before you attempt anything more than simple cuts.