Client had a RHEL 7.2 and SUSE 12 SP2 connected to a secondary hub that was using a tunnel to connect back to the primary. From the primary trying to open up IM or AC2 to the robots you would get a communication error.
Client Linux admin had enabled: tcp_tw_recycle and tcp_tw_reuse
by setting these values to 1 in the OS configuration for IPV4 TCP files
UIM 8.51 Robot 7.93 RHEL 7.2 SUSE 12 SP2
When the client changed these system setting back to 0 from 1 and restarted the machine the communication to the robots would then work.