There are a lot of situations when the station may not connect to the Application Server.
However, here a few points to check:
1) check 10024 and 10025 ports. 10024 port on processing server shall be opened for incoming connection on a machine with processing server,
10025 shall be opened for incoming connection on a machine with processing station (http://help.abbyy.com/en-us/flexicapture/12/admin_guide/architecture_ag)
3) Proxy settings. Keep in mind ports mentioned at 1st step.
4) Make sure that Application Server was setup in Network Host with his IP or DNS name