This issue generally occurs if the QXP Server port is blocked through a firewall (network or local machine).
Open the QXP Server port in the firewall (the default port used by QXPS is 8080).
Add <SUBMIT_USE_PROXY allow='y'/> to the general section of the gluon_config. file, which is located in the LiveEdit/Config folder. If the parameter is already there, change its value to Y from N.
If this value is set to Y, the QXP Server port can remain closed on the firewall and the clients will still be able to establish a connection.