POE needs:
Properly grounded racks - Which, BTW, is the national code requirement
On-Line Double-Conversion UPS' - Line interactive units don't hold up so well with the POE midplanes
460's and 470's have POE firmware available. Verify you have it on the boxes, along with the latest diags and software.
Other notes:
Put your switches in pure 802.3af mode rather than support legacy.
Verify your patch cords are not on the 'wanted' list for faulty conductors with improper coatings. It could cause corrosion of the individual switch ports. There have been multiple recalls of cables, ends, and patch cords that are not meeting the standards but have labels stating they do. The problem is getting quite severe in the industry the past three years. BTW, this does not even include those knockoffs that keep showing up all the time.
TankII