I think its not an zitem error, because he can connect to it with the debug login,
Check in the database if there are the right port number for the server [6000 standard]
Some OLD procedures of the locator put in 8900 as port in the table serverstatus
And other option can be that there is an IP range in the BlockCountryCode thats match to your IP, so you cannot connect if the Countryfilter is enabled.
So go in to your database and check it. I hope this will help you!!