I faced a issue while deleted few domains from Plesk 8.6.
Error While deleting a domain from Plesk :
Unable to remove hosting: Unable to delete system user: SysUser->systemRemove() failed: usermng failed: Unknown error 0xC00CE558 (COM Error C00CE558) at execute command del” while deleting the domains
Every domains showed a COM error when tried to delete it. Here is a fix which I found :
Find a file name “DeferredRemovalStorage.xml” under directory %plesk_dir%\etc\ open it in notepad and you will see it empty, add the code as in the file and save :
<?xml version=”1.0″ encoding=”UTF-8″ standalone=”no” ?>
Now you will be able to delete the domains fine. If it still not work you can try
mchk.exe --domain --domain-name=domain.com --fix=all