Hi Guys,
after one week, I'm back and I tried again to run 2 GPU and 2 CPU tasks simultaneously.
I re-read all the comments of the last 10 days. I tried again with an updated app_info.xml (now with 7.05 instead of 6.56).
I ensured that the cache was not empty when I put the app_info.xml file into the project directory.
Afterwards I stopped and restarted Boinc.
By the next update the message related to the "anonymous platform" came again.
During the last week-end, I detached the host from the project and I re-attached it again, ensuring that the project directory has been fully refreshed for this host.
Since I am unable to understand what happens, I have the feeling to be totally stupid.
Some of the comments showed that I am probably not alone with this very frustrating (and time consuming) issue.
I would appreciate if the tech-team could provide accurate and reliable reference information regarding the simultaneous computation of several GPU tasks, e.g.: app_info.xml, client_state.xml, etc.

Cheers,
Yves

First thing I recommend is to update boinc to 7.0.36
http://boinc.berkeley.edu/dev/forum_thread.php?id=6698&nowrap=true#45639
There are newer versions out but I haven't run them above .36 yet so YMMV if you chose to use them.

Here is the syntax for your app_info file to run 2 tasks simultaneously.

<app_info>
<app>
<name>hcc1</name>
<user_friendly_name>Help Conquer Cancer</user_friendly_name>
</app>
<file_info>
<name>wcg_hcc1_img_7.05_windows_intelx86__ati_hcc1</name>
<executable/>
</file_info>
<file_info>
<name>hcckernel.cl.7.05</name>
<executable/>
</file_info>
<app_version>
<app_name>hcc1</app_name>
<version_num>705</version_num>
<platform>windows_intelx86</platform>
<plan_class>ati_hcc1</plan_class>
<avg_ncpus>1.0</avg_ncpus>
<max_ncpus>1.0</max_ncpus>
<coproc>
<type>ATI</type>
<count>.50</count>
</coproc>
<file_ref>
<file_name>wcg_hcc1_img_7.05_windows_intelx86__ati_hcc1</file_name>
<main_program/>
</file_ref>
<file_ref>
<file_name>hcckernel.cl.7.05</file_name>
<open_name>hcckernel.cl</open_name>
</file_ref>
</app_version>
</app_info>
Copy and paste it into notepad and then rename it app_info.xml

You must download tasks without the app_info file in the project folder first. After you do that, shut down boinc, place the app_info.xml file into the WCG project folder and restart boinc.
I don't know if there will be any real advantage running 2 tasks at a time on your card. Run 1 tasks without the app_info and see what the run time looks like. Add the app_info file and check to see how long it takes to finish 2. Anything less than twice as long for 2 is ok. Anything equal to or more than twice as long is wasting resources.
Once you place the app_info file into the project folder and restart boinc you should finish any tasks that are in your cache if you decide to remove it. If you remove the file with unfinished tasks they will be lost.
Hope this helps you.

That's a good point. ATI driver support for OpenCL on XP stopped a while back so that could be the problem.

Dont think so because it is only 1 gb used. HD activity is nearly zero.

i dont understand what it has to do with virtual memory when the physical is long away to be full and nearly no HD activity that would indicate for swapping ^^ But ok i understand when the memorycommunication is not fast enough for this card. Then i cant change anything of it (MB dont support OC). So its like POEM then, it wants memorybandwidth too like hell ^^