Here is the backtrace:
<div style='word-wrap: break-word; border: 3px solid red; padding:4px;
width:70%; background-color:#FFFF96;'> <strong>There is an error. Please
report the message (Piwik 1.8.2) and full backtrace in the <a
href='?module=Proxy&action=redirect&url=http://forum.piwik.org'
target='_blank'>Piwik forums</a> (please do a Search first as it might have
been reported already!).<br /><br/> Warning:</strong> <i>Invalid argument
supplied for foreach()</i> in <b>/home/piwik/www/plugins/API/API.php</b> on
line <b>965</b><br /><br />Backtrace --><div style="font-family:Courier;
font-size:10pt">#0 Piwik_ErrorHandler(...) called at
[/home/piwik/www/plugins/API/API.php:965]#1 Piwik_API_API->get(...) called
at [:]#2 call_user_func_array(...) called at
[/home/piwik/www/core/API/Proxy.php:190]#3 Piwik_API_Proxy->call(...)
called at [/home/piwik/www/core/API/Request.php:128]#4 Piwik_API_Request->
process(...) called at [/home/piwik/www/core/ViewDataTable.php:421]#5
Piwik_ViewDataTable->loadDataTableFromAPI(...) called at
[/home/piwik/www/core/ViewDataTable/GenerateGraphData/ChartEvolution.php:109]#6
Piwik_ViewDataTable_GenerateGraphData_ChartEvolution->
loadDataTableFromAPI(...) called at
[/home/piwik/www/core/ViewDataTable/GenerateGraphData.php:181]#7
Piwik_ViewDataTable_GenerateGraphData->main(...) called at
[/home/piwik/www/core/Controller.php:247]#8 Piwik_Controller->
getLastUnitGraphAcrossPlugins(...) called at
[/home/piwik/www/plugins/VisitsSummary/Controller.php:78]#9
Piwik_VisitsSummary_Controller->getEvolutionGraph(...) called at [:]#10
call_user_func_array(...) called at
[/home/piwik/www/core/FrontController.php:138]#11 Piwik_FrontController->
dispatch(...) called at [/home/piwik/www/core/FrontController.php:159]#12
Piwik_FrontController->fetchDispatch(...) called at
[/home/piwik/www/core/ViewDataTable/GenerateGraphHTML.php:170]#13
Piwik_ViewDataTable_GenerateGraphHTML->getGraphData(...) called at
[/home/piwik/www/core/ViewDataTable/GenerateGraphHTML.php:125]#14
Piwik_ViewDataTable_GenerateGraphHTML->buildView(...) called at
[/home/piwik/www/core/ViewDataTable/GenerateGraphHTML.php:109]#15
Piwik_ViewDataTable_GenerateGraphHTML->main(...) called at
[/home/piwik/www/core/Controller.php:247]#16 Piwik_Controller->
getLastUnitGraphAcrossPlugins(...) called at
[/home/piwik/www/plugins/VisitsSummary/Controller.php:78]#17
Piwik_VisitsSummary_Controller->getEvolutionGraph(...) called at
[/home/piwik/www/plugins/VisitsSummary/Controller.php:23]#18
Piwik_VisitsSummary_Controller->index(...) called at [:]#19
call_user_func_array(...) called at
[/home/piwik/www/core/FrontController.php:138]#20 Piwik_FrontController->
dispatch(...) called at [/home/piwik/www/index.php:53]