Hello Jancolle!

The devs made some tests on the account you provided us with and gave the following response:

While unable to reproduce the "The ZeXtras Chat server is not installed or is currently disabled." error, we noticed that your proxy is dropping HTTP connections 20 seconds after those have been established, while the ZeXtras Chat Zimlet uses a 30-second ping cycle for presence and push communication. This causes ZxChat's ping requests to be dropped with a "502" http error, causing ZeXtras Chat to be unusable.

Reconfiguring your proxy to wait 31 seconds instead of 20 before dropping a connection should solve the issue.

Have a nice day,
Cine
the ZeXtras Team