This has been asked before plenty of times, a quick search on CSC will provide all the pointers to fix this.
Notice you're officially not supported as that version is not supported on W8.1
http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cipc/8_6_4/CIPC_BK_C6B0FEBA_00_cisco-ip-communicator-864-release.html#CIPC_RF_A5233D61_00
HTH
java
if this helps, please rate