Same disk, two different errors on two different drives.

[brellyn]

on my Pioneer BD-209m
Error 'Scsi error - MEDIUM ERROR:L-EC UNCORRECTABLE ERROR' occurred while reading '/BDMV/STREAM/00051.m2ts' at offset '941162496'

on my Pioneer BD-209d
Error 'Scsi error - MEDIUM ERROR:L-EC UNCORRECTABLE ERROR' occurred while reading '/BDMV/STREAM/00051.m2ts' at offset '872411136'

thoroughly cleaned with Dawn, then eyeglass cleaner (which works well for me) and same errors.

granted the disk is probably bad (though the surface is pristine), why different errors? Shouldn't a bad spot be a bad spot no matter which drive is reading it?

[Woodstock]

Differences in the optics of the drives. Tolerances for laser angle and wavelength are pretty darn tight, but they're tolerances just the same. A slight difference in either can make a section of a disk readable or unreadable.

I see this more with DVDs being read in BD drives. 99.99% of the time it's fine, but occasionally you encounter a disk that can ONLY be read in a DVD player, because of the different wavelength light. I keep 2 different portable DVDs handy for when that happens.

You MIGHT be able to get this disk read by increasing the retry count in Preferences->IO; it's worth a try.