Cannot change client limits due to "remove webserver" error

Hi all!

I am trying to increase my clients limits but I got the following error message:
"The server you are trying to remove from this client is used as a webserver. Be sure that this server is not used by this client before you remove it."

I have turned on debugging but found nothing only this:

Mon Feb 10 14:30:01 CET 2020 10.02.2020-14:30 - DEBUG - Calling function 'check_phpini_changes' from plugin 'webserver_plugin' raised by action 'server_plugins_loaded'.
Mon Feb 10 14:30:01 CET 2020 10.02.2020-14:30 - DEBUG - Remove Lock: /usr/local/ispconfig/server/temp/.ispconfig_lock

The clients, everything has been created with an original "ISPConfig Migration Toolkit" bought here: https://www.ispconfig.org/add-ons/ispconfig-migration-tool/

Does anyone have any suggestions how can I find out what causing the problem ( I think it can be a web_domain problem?)

 

One more thing: This case effects only one client. All the other clients' limits are changeable, working good

 

Thank You very much, problem solved! Thanks for the help, have a nice day!