This worked for me on several boxes running CC 5.2.13

Problem : a few computers could still connect SZTAKI, several others complained :

- Network error: couldn't connect to server
- Scheduler list fetch failed: http error
- Master file fetch failed

The cause must have been on server side as it started on all boxes at about the same time. The problem was persistent on those boxes whereas all others did not have any problem at all.

My solution was cleaning the SZTAKI section in client_state.xml by removing those 4 tags :

<nrpc_failures>
<min_rpc_time>
<master_url_fetch_pending/>
<sched_rpc_pending/>

I am not sure if they all had to be removed but what I did worked :-)

My guess would be, that <master_url_fetch_pending/> and <sched_rpc_pending/> together bring the core client into a situation that it cannot solve by itself anymore.