At present Avalanche on Spirent Test Center requires Active State TCL version 8.4.13
detail: Spirent Test Center requires TCL to be present in order for management communication to take place – If you are performing and upgrade chances are you have TCL already installed and searching you system for TCLSH84.EXE will provide you with the location that the avalanche GUI requires for initialization. The Default location is in the TCL directory – listed “something” like this: C:\Program Files\Spirent Communications\Spirent TestCenter 3.50\TCL\bin – The version may be different. If you have not installed TCL to this point you can download it from the customer support Website - support.spirentcom.com -> downloads -> Spirent Test Center -> TCL 8.4.13 (configured for Spirent TestCenter Automation)