Error in download widget at dashboard after updating to v1.9.1


I just updated a high traffic site to version 1.9.1 (from 1.6).
I unzupped the downloaded zip file to the installation directory and did the database update at the commandline, as Piwik told me to do.
In genereal everything worked fine, but the download widget at the dashboard isn´t working anymore.
The list contains the domains, if I klick an an entry to expand it, I get the following error (taken from error log)

Then I deleted everyhthing in piwik/tmp the templates have been created new, but the error still exists.

[hostname is removed]

There is an error. Please report the message (Piwik 1.9.1) and full backtrace in the Piwik forums (please do a Search first as it might have been reported already!).
Notice: Undefined index: nbColumns in …/htdocs/apps/piwik/tmp/templates_c/%%41^416^416F4DD8%%datatable_actions_subdatable.tpl.php on line 12
Backtrace -->
#0 Piwik_ErrorHandler(…) called at […/htdocs/apps/piwik/tmp/templates_c/%%41^416^416F4DD8%%datatable_actions_subdatable.tpl.php:12]
#1 include(…) called at […/htdocs/apps/piwik/libs/Smarty/Smarty.class.php:1263]
#2 Smarty->fetch(…) called at […/htdocs/apps/piwik/core/View.php:133]
#3 Piwik_View->render(…) called at […/htdocs/apps/piwik/core/Controller.php:153]
#4 Piwik_Controller->renderView(…) called at […/htdocs/apps/piwik/plugins/Actions/Controller.php:341]
#5 Piwik_Actions_Controller->getDownloadsSubDataTable(…) called at [:]
#6 call_user_func_array(…) called at […/htdocs/apps/piwik/core/FrontController.php:138]
#7 Piwik_FrontController->dispatch(…) called at […/htdocs/apps/piwik/index.php:53]

The post data are:
action getDownloadsSubDataTable
controllerActionCalledWhenRequestSubTable getDownloadsSubDataTable
enable_sort 1
filter_limit 100
filter_sort_column nb_visits
filter_sort_order desc
idSubtable 23
keep_summary_row 0
module Actions
search_recursive 1
totalRows 2
viewDataTable table

raw request:

Anything I missed at the update?

Just installing an update is not the first option, cause I have to go through a deployment process, that will take a while.