Sometimes it is not possible to access Parallels Plesk Panel. Browser displays following error:

[box style=’error’]ERROR: SWKeyExFatalError

xmlrpc error: Expected <param> to have 1 children, found 0

0: common_func.php3:4524
of_get_key_by_product(string ‘plesk-win’)
1: common_func.php3:4524
2: common_func.php3:4603
getKeyProp(string ‘demo’)
3: auth.php3:54[/box]

The above error seems that registry.xml file may have gone corrupted.

Resolution of above error is very simple:
Check the size of the file %plesk_dir%\admin\repository\registry.xml. If the file is empty and its size equals to 0KB, delete this file.
Once it is deleted, try to access Parallels Plesk Panel again. A new file should be generated automatically.