If it does not have Subtitles, set ps3 media server up to use TSmuxer first.
http://img.techpowerup.org/100608/ps3media.png
Move it to the top of the list, save, and restart. PS3MS will no longer transcode thing the PS3 can read natively.
That cpu is not enough to transcode 1080p on the fly without stuttering, unless you decide to lower quality.
See above for no trancoding.
And it's because a PS3 doesn't have Windows DRM stuff built in. Could be a simple issue of unrecognized player, or it could be a DRM encumbered file. Either way, the built in styrsming service in Windows is junk.
Quality is lower, and doesn't handle styled subs properly.