The PLCs with operation system BECK and runtime to version V20150213 may show the problem with stopped network communication. Program is still running but PLC is not available to ping command. This problem is caused by constant reconnection of other client. Typically it could be caused by operating terminal HT100 (to FW version 9) or by providing public IP address connection directly on PLC. After some time there is problem with lack off memory. First help is turn off / on device.
This problem is fixed in new version FW version 10 for HT100 (upload from web interface). It is also necessary to upload new runtime version V20150415. New version SoftPLC IDE download here. New version for HT100 is available here.