Piwik login error

Grettings all. My apologies in advance if this question has already been answered. I’m trying to set up Piwik 1.11 for the first time and get the error below when trying to log in. I am completely new to Piwik. Thanks in advance for any responses.

[size=small]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!).

[size=small]Warning: Cannot modify header information - headers already sent by (output started at /dweb/httpd/support-stats/analytics/libs/Zend/Log/Writer/Stream.php:133) in /dweb/httpd/support-stats/analytics/core/Common.php on line 1670

Backtrace -->

#0 Piwik_ErrorHandler(…) called at [:]
#1 header(…) called at [/dweb/httpd/support-stats/analytics/core/Common.php:1670]
#2 Piwik_Common::sendHeader(…) called at [/dweb/httpd/support-stats/analytics/core/Cookie.php:161]
#3 Piwik_Cookie->setCookie(…) called at [/dweb/httpd/support-stats/analytics/core/Cookie.php:197]
#4 Piwik_Cookie->save(…) called at [/dweb/httpd/support-stats/analytics/plugins/Login/Login.php:141]
#5 Piwik_Login->initSession(…) called at [:]
#6 call_user_func_array(…) called at [/dweb/httpd/support-stats/analytics/libs/Event/Dispatcher.php:284]
#7 Event_Dispatcher->postNotification(…) called at [/dweb/httpd/support-stats/analytics/core/PluginsManager.php:722]
#8 Piwik_PostEvent(…) called at [/dweb/httpd/support-stats/analytics/plugins/Login/Controller.php:158]
#9 Piwik_Login_Controller->authenticateAndRedirect(…) called at [/dweb/httpd/support-stats/analytics/plugins/Login/Controller.php:70]
#10 Piwik_Login_Controller->login(…) called at [/dweb/httpd/support-stats/analytics/plugins/Login/Controller.php:45]
#11 Piwik_Login_Controller->index(…) called at [:]
#12 call_user_func_array(…) called at [/dweb/httpd/support-stats/analytics/core/FrontController.php:136]
#13 Piwik_FrontController->dispatch(…) called at [/dweb/httpd/support-stats/analytics/core/Controller.php:727]
#14 Piwik_Controller->redirectToIndex(…) called at [/dweb/httpd/support-stats/analytics/plugins/CoreHome/Controller.php:41]
#15 Piwik_CoreHome_Controller->redirectToCoreHomeIndex(…) called at [:]
#16 call_user_func_array(…) called at [/dweb/httpd/support-stats/analytics/core/FrontController.php:136]
#17 Piwik_FrontController->dispatch(…) called at [/dweb/httpd/support-stats/analytics/index.php:52][/size][/size]

Delete all files and upload the latest beta 1.12-b7 instead: Index of /