No video/audio on some DVB-C channels

[brunoh]

MediaPortal Version: MP 0.2+svn 12062
MediaPortal Skin: Blue Two
Windows Version: XP MCE SP2
CPU Type: Intel 3Ghz
HDD: Seagate 160 GB
Memory: 2 GB
Motherboard: Dell Dimension
Motherboard Chipset:
Motherboard Bios: Dell A04
Video Card: ATI X600
Video Card Driver: Ati Catalyst 6.11
Sound Card: internal SigmaTel
Sound Card AC3:
Sound Card Driver: 5.10.0.4823
1. TV Card: Floppy DTV
1. TV Card Type: DVB-C
1. TV Card Driver: 4.2
2. TV Card: Twinhan
2. TV Card Type: DVB-C
2. TV Card Driver: 1.2.3.8
3. TV Card: Hauppauge pvr-350
3. TV Card Type: analog
3. TV Card Driver: 1.18.21.23257
4. TV Card:
4. TV Card Type:
4. TV Card Driver:
MPEG2 Video Codec: Ati MPEG Video Decoder
MPEG2 Audio Codec: Dscaler
Satelite/CableTV Provider:
HTPC Case: Dell Dimension 400/9150
Cooling:
Power Supply:
Remote: FireDtV
TV: Dell 2405FPW
TV - HTPC Connection: DVI

My experience with the new tvserver has improved a lot since the last view revisions. I had problems with timeshifting and channel changes. This now works much better.
However I have still some problems:

When I scan for dvb-c channels it finds all my channels. But on some channels (about 10%), I do not get audio or video, it just times out and gives "no video/audio detected".

When I check the table tuningdetail for this channels, I see that the column pcrPid for these nonworking channels is 0.
The problem occours when I try to watch these channels on the FloppyDTV and on the Twinhan DTV-DVBC 878.

The same channels work with mytheatre on the floppydtv and with twinhandtv on my twinhan.

From the server log, I think the line with the problem is: "no pmt received yet"

I attach the corresponding part of tv.log

Thank you very much