I have checked the event viewer and I cannot find anything there.
Also checked the Plesk\admin\logs files and also no errors there, besides this one (php_error.log):
[14-Dec-2011 11:14:04] Exception: PHP Warning: json_encode() [<a href='function.json-encode'>function.json-encode</a>]: Invalid UTF-8 sequence in argument; File: C:\Program Files (x86)\Parallels\Plesk\admin\plib\Zend\Json.php, Line: 146
file: C:\Program Files (x86)\Parallels\Plesk\admin\smb\application\library\Smb\Exception\Syntax.php
line: 60
code: 0
trace: #0 [internal function]: Smb_Exception_Syntax::handleError(2, 'json_encode() [...', 'C:\Program File...', 146, Array)
#1 C:\Program Files (x86)\Parallels\Plesk\admin\plib\Zend\Json.php(146): json_encode(Array)
#2 C:\Program Files (x86)\Parallels\Plesk\admin\panel\application\controllers\ServerController.php(34): Zend_Json::encode(Array)
#3 C:\Program Files (x86)\Parallels\Plesk\admin\plib\Zend\Controller\Action.php(513): ServerController->toolsAction()
#4 C:\Program Files (x86)\Parallels\Plesk\admin\plib\Zend\Controller\Dispatcher\Standard.php(295): Zend_Controller_Action->dispatch('toolsAction')
#5 C:\Program Files (x86)\Parallels\Plesk\admin\plib\Zend\Controller\Front.php(954): Zend_Controller_Dispatcher_Standard->dispatch(Object(Zend_Controller_Request_Http), Object(Zend_Controller_Response_Http))
#6 C:\Program Files (x86)\Parallels\Plesk\admin\panel\application\library\AdminPanel\Application\Web.php(25): Zend_Controller_Front->dispatch()
#7 C:\Program Files (x86)\Parallels\Plesk\admin\panel\application\public\index.php(20): AdminPanel_Application_Web->run()
#8 {main}
[14-Dec-2011 11:14:06] PHP Warning: json_encode() [<a href='function.json-encode'>function.json-encode</a>]: Invalid UTF-8 sequence in argument; File: C:\Program Files (x86)\Parallels\Plesk\admin\plib\Zend\Json.php, Line: 146
[14-Dec-2011 11:14:06] Exception: PHP Warning: json_encode() [<a href='function.json-encode'>function.json-encode</a>]: Invalid UTF-8 sequence in argument; File: C:\Program Files (x86)\Parallels\Plesk\admin\plib\Zend\Json.php, Line: 146
file: C:\Program Files (x86)\Parallels\Plesk\admin\smb\application\library\Smb\Exception\Syntax.php
line: 60
code: 0
trace: #0 [internal function]: Smb_Exception_Syntax::handleError(2, 'json_encode() [...', 'C:\Program File...', 146, Array)
#1 C:\Program Files (x86)\Parallels\Plesk\admin\plib\Zend\Json.php(146): json_encode(Array)
#2 C:\Program Files (x86)\Parallels\Plesk\admin\panel\application\controllers\ServerController.php(34): Zend_Json::encode(Array)
#3 C:\Program Files (x86)\Parallels\Plesk\admin\plib\Zend\Controller\Action.php(513): ServerController->toolsAction()
#4 C:\Program Files (x86)\Parallels\Plesk\admin\plib\Zend\Controller\Dispatcher\Standard.php(295): Zend_Controller_Action->dispatch('toolsAction')
#5 C:\Program Files (x86)\Parallels\Plesk\admin\plib\Zend\Controller\Front.php(954): Zend_Controller_Dispatcher_Standard->dispatch(Object(Zend_Controller_Request_Http), Object(Zend_Controller_Response_Http))
#6 C:\Program Files (x86)\Parallels\Plesk\admin\panel\application\library\AdminPanel\Application\Web.php(25): Zend_Controller_Front->dispatch()
#7 C:\Program Files (x86)\Parallels\Plesk\admin\panel\application\public\index.php(20): AdminPanel_Application_Web->run()
#8 {main}
But don't know if it's related to this issue.