Error: Permission denied to remove subdomain ID XX

Hello.
I created a new subdomain on my server running Plesk 12.5.30 and changed manually the folder where the website files are stored.
I changed my mind and want to delete the subdomain, but I get the error:
Error: Permission denied to remove subdomain ID XX
with XX the ID of the subdomain.
I checked the permissions and changed them to be like for the other domains and subdomains, but with no effect.
I deleted the folder manually with the same result.
I tried many variatins of file...

Error: Permission denied to remove subdomain ID XX