Forbidden magic and ars magica are having a hard time playing nice with each other. It seems that I cant get forbidden magic to allow for witchwood cores or vinteum caps with AM2 installed. I'm haven't been able to find a player beacons version with 1.7.10 that doesn't crash so I haven't checked compat with those parts.
Versions
AM2 1.4.0.008
Forbidden Magic 1.7.10-0.561
Thaumcraft 4.2.3.5

Go into the FM config. Enable AM2 interaction.