This error happens when your site tried to access phpFox Store and failed.
By default, when you access Admin CP, automatically there will be a connection to phpFox Store first to check for app updates, availability...
However, if the server of your phpFox site is unable to connect to the store server at that time, this error will shows up.
To resolve this issue, first of all, we suggest you to wait a little bit and then try again.
As in some cases, store server could be overloaded with requests and result to a disconnection on your request OR your server has some obstacles while connect to the store server.
Wait a little bit until the connection on server is stable could solve the issue entirely without any further action.
If the issue continue persisting on your phpFox site, we suggest you to contact your hosting provider and ask for the reason why your site server is unable to connect to store server.
It could be a firewall issue, wrong configuration on server settings... Your hosting provider can help you to figure this out and resolve the connection.