Thanks, for your reaction.
I have renamed the file extentions in VOB.
Same result : you can not import many files : before 100 files the error appears.

I tried the demo intemediate codec CineForm Neoscene.
Big files (but nice editing !), but these files are loading without problems (I tried about 100 files).

So I think Movie Studio does not like the (proxy) files generated by the Sony PMB application. A Sony camera, Sony PMB software and Sony Movie Studio, till now it seems not to be a good combination...... The Sony official support came with the standard solutions referring to the (different) topics with low memory errors when rendering or editing.

I am still finding out the best workflow. I will try other (free) transcoder software to generate the low resolution files. If it is possible I will preserve the 5.1 sound. Maybe Movie Studio has less bugs withe other file formats.

If I find a solution that is working, I will let you know.


MediaInfo data of the MPG files (from Sony PMB) :
Format : MPEG-PS
File size : 9,07 MiB
Duration : 10s 880ms
Overall bit rate : 6 995 Kbps

Video
ID : 224 (0xE0)
Format : MPEG Video
Format version : Version 2
Format profile : Main@Main
Format settings, BVOP : Ja
Format settings, Matrix : Standaard
Format settings, GOP : M=3, N=12
Duration : 10s 840ms
Bit rate mode : Constant
Bit rate : 6 408 Kbps
Nominal bit rate : 6 000 Kbps
Width : 720 pixels
Height : 576 pixels
Display aspect ratio : 16:9
Frame rate : 25,000 fps
Standard : PAL
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Interlaced
Scan order : Bovenste Veld Eerst
Bits/(Pixel*Frame) : 0.618
Stream size : 8,28 MiB (91%)

Audio
ID : 128 (0x80)
Format : AC-3
Format/Info : Audio Coding 3
Mode extension : CM (complete main)
Duration : 10s 880ms
Bit rate mode : Constant
Bit rate : 448 Kbps
Channel(s) : 6 kanalen
Channel positions : Front: L C R, Side: L R, LFE
Sampling rate : 48,0 KHz
Bit depth : 16 bits
Video delay : -80ms
Stream size : 595 KiB (6%)

I found a solution (workaround) to make the low resolution proxy files with the original 5.1 (ac3) sound and without the Moviestudio memory error when loading many files.

I tested a lot with transcoding the original files (with the program FFMPEG).
I made files that are fully compliant with the standards and "specials".
In general there are 2 problems with 5.1 sound :
- not all the combinations of file containers and codecs are valid or are recognised by Moviestudio (like an avi with DV video (MJPEG) and 5.1 (AC3) or multichannel PCM sound or mpg files with multichannel PCM sound);
- the (valid) mpg combinations (extention .mpg) with 5.1 AC3 sound have the Moviestudio memory error (bug) when importing many of them (memory error with more then about 80 files).

So I tried another combination of file containers and codecs.
I used the program tsMuxerGUI / tsMuxeR (commandline) and made a MPEG2 transport stream container (extention .ts) with the video of the low resolution mpg file (from PMB exported) and the 5.1. AC3 sound from the original mts (camera) file. This combination edits smooth and doesn't have the memory error with many files !

To verify I made 3 x 300 test files :
(1) low resolution .mpg direct export from the program Sony PMB (came with my camera) ;
(2) video from low resolution .mpg file and AC3 audio from original (camera) .mts file, muxed in a .ts (transport stream) file;
(3) video from low resolution .mpg file, AC3 audio from original (camera) .mts file and PGS (data) from original (camera) .mts file, muxed in a .ts (transport stream) file.

Combination (1) gives the memory error, the combinations (2) and (3) give no memory errors and are playing smoother with transitions.

So, my advice, if you want low resolution copies of your AVCHD camera files (for proxy editing) with 5.1 sound and you want to edit quick and smooth then the best way in Moviestudio seems to be to use the MPEG2 transport stream , *.ts file format.
If you don't have a memory error when importing many (> 100) mpg files with ac3 (5.1) sound, than you are the lucky one and you can forget all of this in this post. If you computer is fast enough to edit the HD (5.1) camera files native, then be happy.

The program tsMuxerGUI / tsMuxeR (commandline) can do the (de)multiplexing for you. Because the video and the audio contents is not changed the demuxing - muxing proces is very fast. With the commandline version and scripting the process can be automated. I think there are other programs (video converters) who can do it for you with more comfort (some ideas ??; must keep the 5.1 sound).

I hope this information is useful for somebody. I spent a lot of time to find a (free) workaround. I took advantage of all the information and free tools from others, so it is fair to publish my experiences.