WebCron does not work / Archive via browser seems to be broken (no replies)

Hi Community,

I've got some problems with Piwik lately.
* I don't have access to setup a "real" cronjob, I did the archiving always via webcron. But now - when testing the webcron via browser I get an error message I don't understand:

You must specify the Super User token_auth as a parameter to this script, eg. ?token_auth=XYZ if you wish to run this script through the browser.

Well that is what I do: The URL I'm calling seems to be right:

http://my.piwik.domain.com/misc/cron/archive.php?token_auth=1234567890

.. and 1234567890 is the API Key from my super users account. So what to change? Small side question: On the API page the key is given with a leading '&':

&token_auth=1234567890

, NOT with a '?', but it makes no difference, the error occurs anyway.
* As workaround I tried the archiving via browser, but that seems not to work too: No data in the graphs for the most sites, but I can see the visitors log is filled with data.
Can anybody point me in the right direction?

My setup:
Piwik 2.9.1
shared hosting enviroment
All green in Settings -> Systemcheck
But: No LOAD DATA INFILE at all (I've turned it off via config)
150 low traffic sites are tracked.
30 sites get data in the graphs, the rest stays empty.

Thanks a lot.
Chris