[mnewnham]

O/S: Windows XP SP3
CPU: Genuine Intel® CPU 2140 @ 1.60GHz Dual Core 64Bit
RAM: 1Mb
Video: GEForce 8400GD / Driver 6.14.12.7533 / Using HDMI Output
Sound Card: ASUS Xonar DS / Driver 5.12.8.1768 / Using Optical Output
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XBMC: 11.0
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Playing MKV File, after approx 35 minutes, Screen goes black, Garbled sound continues for approximately 30 secs then fails. After reboot, approx further 10 minutes can be watched then fails again. Continue process until end of file.

Rolled system back to version 10. File plays no problem.
Debug log contains entire session from boot to failure.


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Debug log: http://pastebin.com/LuczHmes
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MediaInfo:

General
Unique ID : 195526203685422965041880201322400178492 (0x9318FA208A1439BA8CD93B435EA1E13C)
Complete name : \\Mediaserver\library\Torrents\Lewis.S06E02.HDTV.720p.x264-GTi.mkv
Format : Matroska
Format version : Version 2
File size : 1.59 GiB
Duration : 1h 27mn
Overall bit rate : 2 611 Kbps
Encoded date : UTC 2012-05-24 01:44:56
Writing application : mkvmerge v4.9.1 ('Ich will') built on Jul 11 2011 23:53:15
Writing library : libebml v1.2.1 + libmatroska v1.1.1

Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : [email protected]
Format settings, CABAC : Yes
Format settings, ReFrames : 5 frames
Codec ID : V_MPEG4/ISO/AVC
Duration : 1h 27mn
Bit rate : 2 303 Kbps
Width : 1 280 pixels
Height : 720 pixels
Display aspect ratio : 16:9
Frame rate : 25.000 fps
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.100
Stream size : 1.41 GiB (88%)
Writing library : x264 core 122 r2184 5c85e0a
Encoding settings : cabac=1 / ref=5 / deblock=1:0:0 / analyse=0x3:0x113 / me=umh / subme=8 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=1 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-3 / threads=6 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=2 / b_bias=0 / direct=3 / weightb=1 / open_gop=0 / weightp=2 / keyint=250 / keyint_min=25 / scenecut=40 / intra_refresh=0 / rc_lookahead=50 / rc=crf / mbtree=1 / crf=19.0 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00
Language : English
Default : No
Forced : No

Audio
ID : 2
Format : AC-3
Format/Info : Audio Coding 3
Mode extension : CM (complete main)
Format settings, Endianness : Big
Codec ID : A_AC3
Duration : 1h 27mn
Bit rate mode : Constant
Bit rate : 256 Kbps
Channel(s) : 2 channels
Channel positions : Front: L R
Sampling rate : 48.0 KHz
Bit depth : 16 bits
Compression mode : Lossy
Delay relative to video : 128ms
Stream size : 160 MiB (10%)
Language : English
Default : Yes
Forced : No

Text #1
ID : 3
Format : UTF-8
Codec ID : S_TEXT/UTF8
Codec ID/Info : UTF-8 Plain Text
Title : SRT
Language : English
Default : No
Forced : No

Text #2
ID : 4
Format : SSA
Codec ID : S_TEXT/SSA
Codec ID/Info : Sub Station Alpha
Compression mode : Lossless
Title : SSA
Language : English
Default : No
Forced : No

[MassIV]

You are not alone. The bug seems to be in ffmpeg. And affects any program that uses it.
Maybe using a portable Dharma v10 could keep you busy while we wait for the good news.