Htmlspecialchars() error (w/ backtrace)

There is an error. Please report the message (Piwik 1.11.1) and full backtrace in the Piwik forums (please do a Search first as it might have been reported already!).

Warning: htmlspecialchars() [function.htmlspecialchars]: Invalid multibyte sequence in argument in /home/benbra/CafeNebulus/piwik/core/DataTable/Filter/SafeDecodeLabel.php on line 53

Backtrace -->

#0 Piwik_ErrorHandler(…) called at [:]
#1 htmlspecialchars(…) called at [/home/benbra/CafeNebulus/piwik/core/DataTable/Filter/SafeDecodeLabel.php:53]
#2 Piwik_DataTable_Filter_SafeDecodeLabel::safeDecodeLabel(…) called at [/home/benbra/CafeNebulus/piwik/core/DataTable/Filter/SafeDecodeLabel.php:70]
#3 Piwik_DataTable_Filter_SafeDecodeLabel->filter(…) called at [/home/benbra/CafeNebulus/piwik/core/DataTable.php:387]
#4 Piwik_DataTable->filter(…) called at [/home/benbra/CafeNebulus/piwik/core/DataTable.php:414]
#5 Piwik_DataTable->applyQueuedFilters(…) called at [/home/benbra/CafeNebulus/piwik/core/API/ResponseBuilder.php:300]
#6 Piwik_API_ResponseBuilder->handleDataTable(…) called at [/home/benbra/CafeNebulus/piwik/core/API/ResponseBuilder.php:78]
#7 Piwik_API_ResponseBuilder->getResponse(…) called at [/home/benbra/CafeNebulus/piwik/core/API/DataTableManipulator.php:142]
#8 Piwik_API_DataTableManipulator->loadSubtable(…) called at [/home/benbra/CafeNebulus/piwik/core/API/DataTableManipulator/Flattener.php:103]
#9 Piwik_API_DataTableManipulator_Flattener->flattenRow(…) called at [/home/benbra/CafeNebulus/piwik/core/API/DataTableManipulator/Flattener.php:124]
#10 Piwik_API_DataTableManipulator_Flattener->flattenRow(…) called at [/home/benbra/CafeNebulus/piwik/core/API/DataTableManipulator/Flattener.php:124]
#11 Piwik_API_DataTableManipulator_Flattener->flattenRow(…) called at [/home/benbra/CafeNebulus/piwik/core/API/DataTableManipulator/Flattener.php:124]
#12 Piwik_API_DataTableManipulator_Flattener->flattenRow(…) called at [/home/benbra/CafeNebulus/piwik/core/API/DataTableManipulator/Flattener.php:124]
#13 Piwik_API_DataTableManipulator_Flattener->flattenRow(…) called at [/home/benbra/CafeNebulus/piwik/core/API/DataTableManipulator/Flattener.php:124]
#14 Piwik_API_DataTableManipulator_Flattener->flattenRow(…) called at [/home/benbra/CafeNebulus/piwik/core/API/DataTableManipulator/Flattener.php:124]
#15 Piwik_API_DataTableManipulator_Flattener->flattenRow(…) called at [/home/benbra/CafeNebulus/piwik/core/API/DataTableManipulator/Flattener.php:69]
#16 Piwik_API_DataTableManipulator_Flattener->doManipulate(…) called at [/home/benbra/CafeNebulus/piwik/core/API/DataTableManipulator.php:85]
#17 Piwik_API_DataTableManipulator->manipulate(…) called at [/home/benbra/CafeNebulus/piwik/core/API/DataTableManipulator/Flattener.php:53]
#18 Piwik_API_DataTableManipulator_Flattener->flatten(…) called at [/home/benbra/CafeNebulus/piwik/core/API/ResponseBuilder.php:284]
#19 Piwik_API_ResponseBuilder->handleDataTable(…) called at [/home/benbra/CafeNebulus/piwik/core/API/ResponseBuilder.php:78]
#20 Piwik_API_ResponseBuilder->getResponse(…) called at [/home/benbra/CafeNebulus/piwik/core/API/Request.php:129]
#21 Piwik_API_Request->process(…) called at [/home/benbra/CafeNebulus/piwik/core/ViewDataTable.php:431]
#22 Piwik_ViewDataTable->loadDataTableFromAPI(…) called at [/home/benbra/CafeNebulus/piwik/core/ViewDataTable/HtmlTable.php:80]
#23 Piwik_ViewDataTable_HtmlTable->main(…) called at [/home/benbra/CafeNebulus/piwik/plugins/Actions/Controller.php:464]
#24 Piwik_Actions_Controller->configureGenericViewActions(…) called at [/home/benbra/CafeNebulus/piwik/plugins/Actions/Controller.php:406]
#25 Piwik_Actions_Controller->configureViewActions(…) called at [/home/benbra/CafeNebulus/piwik/plugins/Actions/Controller.php:46]
#26 Piwik_Actions_Controller->getPageUrls(…) called at [:]
#27 call_user_func_array(…) called at [/home/benbra/CafeNebulus/piwik/core/FrontController.php:136]
#28 Piwik_FrontController->dispatch(…) called at [/home/benbra/CafeNebulus/piwik/index.php:52]

WHat version of pHP do you use? can you try upgrading to latest 5.3 or latest 5.4 versions?