How to cut out 20 min in the middle from mkv file

[chros]

I have an mkv file wich hold xvid video and aac audio. I have tried the splitting feature in mkvmergegui, and it works ok, if I want to cut a part from the beginning, but if I want to cut in the middle: eg. from time 00:34:32 (max number of files is 2), the resulted 2nd part is playable, but unwatchable (I think it doesn't cut at keyframe).

So I have tried to search the keyframe with mkvinfo, and I get:
| + Block group
| + Block (track number 1, 1 frame(s), timecode 2072.003s = 00:34:32.003000000)
| + Frame with size 1098
| + Reference block: -66.000000ms
|+ Cluster
| + Cluster timecode: 2072.070s
| + Block group
| + Block (track number 1, 1 frame(s), timecode 2072.070s = 00:34:32.070000000)
| + Frame with size 870
| + Block group
| + Block (track number 2, 8 frame(s), timecode 2072.107s = 00:34:32.107000000)
| + Frame with size 415
| + Frame with size 406
| + Frame with size 409
| + Frame with size 449
| + Frame with size 454
| + Frame with size 483
| + Frame with size 468
| + Frame with size 465
| + Block group
| + Block (track number 1, 1 frame(s), timecode 2072.137s = 00:34:32.137000000)
| + Frame with size 804
| + Reference block: -67.000000ms

Is the keyframe at 00:34:32.070000000 ? (I have tried it, but the result is the same ...)

Virtualdubmod doesn't open this mkv file: "Matroska stream 1 doesn't have a samplerate" ... (I have muxed this file with mkvmergegui)

Any idea ?
Thanks